This is a list of well-known online encyclopedias that are currently accessible or were formerly accessible on the Internet.
The largest online encyclopedias are general reference works, though there are also many specialized ones. Some online encyclopedias are editions of a print encyclopedia, such as Encyclopædia Britannica, whereas others originated online, such as Wikipedia. Some online encyclopedia use Wikipedia's MediaWiki software or even fork Wikipedia content to create an alternative version.
| Wikipedia | Various (see list here) | General interest, wiki | Active | Free | CC BY-SA 4.0, GFDL | None | None |
| Nupedia | English language | Combined with GNUpedia | Defunct | None | GFDL 1.1 or later | None | None |
| Interpedia | English language | General interest, the first site to propose a free encyclopedia written by users | Defunct | None | Unknown | Free | None |
| Everipedia | English | General interest | Read-only (archived) | Free | CC BY 4.0 | Wikipedia | None |
| Citizendium | English | General interest, wiki | Active | Free, copyleft | CC BY NC SA 3.0 | None | None |
| Conservapedia | English | American conservative and Christianity interests | Active | Free | Unknown | None | None |
| Scholarpedia | English | Articles are written by scholars and Peer review for accuracy | Active | Free | CC BY NC SA 3.0 | None | None |
| Encyclopædia Britannica | English language | General interest | Active | Limited free access and features, subscription for full access | Unknown | None | None |
| Baidu Baike | Chinese language | Collaborative online encyclopedia hosted by the major Chinese search engine company Baidu | Active | Free | Unknown | None | None |
| Enciklopedio Kalblanda | Esperanto | General interest. The first online encyclopedia in Esperanto | Defunct | None | CC BY SA 3.0, GFDL | None | Esperanto Wikipedia |
| EcuRed | Spanish | General interest. Cuban | Active | Free | None | None | None |
| Encyclopedia.com | English | General interest | Active | Free | None | None | None |
| Baike.com | Chinese language | General interest. China's largest wiki | Active | Free | Unknown | None | None |
| Brockhaus Enzyklopädie | German language | General interest | Active | Limited free access and features, subscription for full access | Unknown | None | None |
| Columbia Encyclopedia | English | General interest | Active | FreeSee word search | Unknown | None | None |
| Crnogorska Enciklopedija | Montenegrin | General interest (hopes to encourage a Montenegrin language Wikipedia) | Defunct | None | Unknown | None | None |
| Croatian Encyclopedia | Croatian | General and national encyclopedia | Active | Free | Unknown | None | None |
| Den Store Danske Encyklopædi | Danish language | General interest | Active | Free | Unknown | None | None |
| Digital Universe | English | Collection of articles on educational, cultural, and scientific topics | Defunct | Free | Unknown | None | None |
| Doosan Encyclopedia | Korean language | General interest | Active | Free | Unknown | None | None |
| Ekşi Sözlük | Turkish language | General interest | Active | Free | Unknown | None | None |
| Encarta (1993–2009) | English | General interest | Defunct | None | Unknown | None | None |
| Enciclonet | Spanish | General interest | Active | Limited free access and features, subscription for full access | None | None | None |
| Encyclopædia Britannica 11th Edition (1910–11) | English | General interest | Defunct | Public domain: completely free access from several online sources | None | None | None |
| Encyclopedia of China | Chinese | General interest | Active | Subscription | Unknown | None | None |
| Từ điển bách khoa Việt Nam | Vietnamese | General interest. State-sponsored encyclopedia. | Active | Free | Unknown | None | None |
| Encyklopedia Internautica | Polish language | General interest | Active | Free | Unknown | None | None |
| Enciclopedia Libre Universal en Español | Spanish language | Fork of the Spanish Wikipedia, using wiki software, released under the GFDL | Defunct | Free, copyleft | Unknown | None | None |
| Encyclopædia Universalis | French language | General interest encyclopedia published by Encyclopædia Britannica | Active | Subscription | Unknown | None | None |
| Everything2 | English | General interest, users can submit articles on the topic of essentially anything | Active | Free | None | None | None |
| The Free Dictionary | English, Spanish, German, French, Italian, Chinese, Portuguese, Dutch, Norwegian, Greek, Arabic, Polish, Turkish, Russian | TheFreeDictionary's Encyclopedia draws from various sources, including The Columbia Encyclopedia. | Active | Free | None | None | None |
| GNE | English | General interest articles are released under a GNU license. Formerly GNUpedia. | Defunct | None | Unknown | None | None |
| Gran Enciclopèdia Catalana | Catalan language | General interest | Active | Free | Unknown | None | None |
| Grand Larousse encyclopédique | French | General interest | Active | Free | None | None | None |
| Great Norwegian Encyclopedia | Norwegian (Bokmål) | General interest | Active | Free | CC BY SA 3.0, CC BY NC SA 3.0 | None | None |
| Great Russian Encyclopedia | Russian | General interest | Active | Free | Unknown | None | None |
| Great Soviet Encyclopedia | Russian, English | General interest, often from the former official Soviet viewpoint. | Active | Free | Unknown | None | None |
| Grokipedia | English | General interest, AI-powered | Active | Free | CC BY-SA 4.0 | Wikipedia | None |
| Hamichlol | Hebrew, English | General interest, designed for Haredim | Active | Free. Copyleft: mirror of Wikipedia content; copyright: original content. | Unknown | Wikipedia | None |
| Internetowa encyklopedia PWN | Polish language | General interest | Active | Free | Unknown | None | None |
| Krugosvet (Rus. Кругосвет) | Russian language | General interest. | Active | Free | Unknown | None | None |
| Marathi Vishwakosh | Marathi language | General Interest | Active | Free | Unknown | None | None |
| Marefa | Arabic language | General interest | Active | Free | Unknown | None | None |
| Mawdoo3 | Arabic language | General interest | Active | Free | Unknown | None | None |
| Metapedia | Hungarian, German, English, Spanish, Swedish language, Romanian, Estonian, French, Slovenian, Czech language, Portuguese, Norwegian, Danish language, Greek language, Dutch language | Far right-wing, white nationalist and neo nazi encyclopedia "Metapedia" als nationales Pendant zu "Wikipedia" (i.e "Metapedia" as a nationalist counterpart to "Wikipedia") from: "Report by the NRW Office for the Protection of the Constitution for the year 2008" by the Ministry of Interior of North Rhine-Westphalia. pp. 59f. | Active | Free | Unknown | None | None |
| Meyers Konversations-Lexikon 4. ed. 1888 - 1892 | German | General interest | Defunct | access from several online sources | Unknown | None | None |
| Namuwiki | Korean language | General interest | Active | Free | CC-BY-NC-SA 2.0 KR | Rigveda Wiki | None |
| Nationalencyklopedin | Swedish language | General interest, comprehensive | Active | Subscription | Unknown | None | None |
| New World Encyclopedia | English | Project of the Unification movement | Active | Free. Wikipedia fork. | CC BY SA 3.0, GFDL | Wikipedia | None |
| Oeconomische Encyclopädie (1773-1858) | German | General interest | Defunct | Public domain: completely free access from several online sources | None | None | None |
| Oxford Bibliographies Online | English | Active | Free | Unknown | None | None | |
| Proleksis Encyclopedia | Croatian | General and national encyclopedia | Active | Free with registration | Unknown | None | None |
| Ruwiki | Russian | General interest, forked from Russian Wikipedia during the Russo-Ukrainian war | Active | Free | CC BY-SA 4.0 | Russian Wikipedia | None |
| Rigveda Wiki | Korean language | General interest | Active | Free | CC-BY-NC-SA 2.0 KR | None | None |
| Sarvavijnanakosam | Malayalam | General interest | Active | Free | Unknown | None | None |
| Sogou Baike | Chinese language | Collaborative online encyclopedia hosted by the major Chinese search engine company Sogou | Active | Free | Unknown | None | None |
| Superpedia | Indonesian, Sundanese, Javanese | General interest | Active | Free | Unknown | None | None |
| Susning.nu (2001–09) | Swedish language | A Swedish language wiki | Defunct | None | Unknown | None | None |
| Tamil Encyclopedia | Tamil language | General Interest | Active | Free | Unknown | None | None |
| Treccani | Italian | General interest | Active | Free | None | None | None |
| Veropedia | English, Dutch language, Spanish | Mirrors stable versions of selected English Wikipedia articles | Defunct | None | Unknown | None | None |
| Visuotinė lietuvių enciklopedija | Lithuanian | General interest | Active | Free | Unknown | None | None |
| WIEM Encyklopedia | Polish language | General interest | Active | Free | Unknown | None | None |
| Winkler Prins | Dutch language | General interest, three different age levels | Active | Subscription | Unknown | None | None |
| World Book Encyclopedia | English | General interest | Active | Subscription | Unknown | None | None |
| Klexikon | German | General interest for children aged six to twelve years | Active | Free | CC BY-SA 3.0 | None | None |
| Afro-American Encyclopaedia | English | Classic historical encyclopedia (1895) | Free | |
| Australian Dictionary of Biography | English | Entries on notable Australians who have died | Free | |
| Croatian Biographical Lexicon | Croatian | Multi-volume biographical reference work on notable figures from Croatian history | Free | |
| Deutsche Biographie | German language | Biographies on notable German speaking people | Free | |
| American National Biography | English | Biographies of notable Americans | Subscription | |
| Dictionary of Irish Architects | English | Biographical information on Irish architects from 1720 to 1940 | Free | |
| Kdo byl kdo | Czech language | Biographies on notable Czechs and Slovak people | Free | |
| Österreichisches Biographisches Lexikon 1815–1950 | German language | Biographies on notable Austrians | Free | |
| Oxford Dictionary of National Biography | English | Comprehensive 66-volume reference work on notable figures from British history | Subscription | |
| Dictionary of New Zealand Biography | English, Māori | Entries on notable New Zealanders who have died | Free | |
| Dizionario Biografico degli Italiani | Italian | Biographical Dictionary of Italian People, published by the Istituto dell'Enciclopedia Italiana Treccani | Free |
| Dictionary of Art Historians | English | Covers topics relating to , , and their dictionaries | Free |
| Dictionary of Greek and Roman Antiquities | English | Incorporates text from the 19th-century encyclopedia of the same name. Focuses on topics of cultural and historical Greek and Rome significance. | Free |
| Dictionary of Greek and Roman Biography and Mythology | English | Focuses on topics dealing with Greek and Roman mythology and people | Free |
| Dictionary of Greek and Roman Geography | English | Focuses on topics relating to Greek and Roman geography | Free |
| Enciclopedia Dantesca | Italian | Devoted to Dante Alighieri and his time, by the Istituto dell'Enciclopedia Italiana Treccani | Free |
| The Encyclopedia of Fantasy | English | Free | |
| Encyclopedia Mythica | English | "About >Encyclopedia Mythica". pantheon.org. Retrieved 2021-03-01. | Free |
| Harper's Dictionary of Classical Literature and Antiquities | English | Covers subjects of classical antiquity; text from 1898 | Free |
| The History of Nordic Women's Literature | English, Danish, Swedish | Searchable online English-language version including many biographies | Free |
| Kindlers Literatur Lexikon | German | Online-only since 2009, covers works and writers of world literature | Subscription |
| The Literary Encyclopedia | English | Literature related articles | Subscription |
| Oxford Art Online | English | Visual art; formerly Grove Art Online and The Dictionary of Art. Originally published in 1996 as a 34-volume printed encyclopedia; offered online since 1998. | SubscriptionIn UK, can normally be accessed free via a local library |
| SIKART | English, German, French, Italian | Biographical dictionary and database of Swiss visual art | Free |
| Agropedia | Covers topics related to agriculture in India | ||
| Austria-Forum | German, English | Online database of Austrian culture | Free |
| Banglapedia | Bengali language, English | Bangladesh-related topics | Free |
| The Canadian Encyclopedia | English, French | General interest regarding Canada and Canadiana (original content of the hard copy Canadian Encyclopedia) | Free |
| Chalo Chatu | English | Collaborative online encyclopedia hosted by Chalo Chatu Foundation featuring comprehensive articles on Zambian culture and history, etc. | Free |
| Culinary Heritage of Switzerland | German, French, Italian, Romansh | Online encyclopedia of traditional Swiss cuisine and produce. | Free |
| DEDI | English, Slovene language | Online encyclopedia of the natural and cultural heritage of Slovenia, operated by the Slovenian Academy of Sciences and Arts Scientific Research Center. | Free |
| Dictionary of Sydney | English | Articles on the history and culture of Sydney | Free |
| Encyclopaedia of Islam, 3rd edition | English | About the Islamic world, not a Muslim encyclopedia | Subscription |
| Encyclopædia Iranica | English, plans for a future Persian language version | Topics on Iranology and the influence of the Iranian peoples throughout history | Free |
| The Encyclopaedia of Korea | English | Korea-related topics | Free |
| Encyclopedia of Korean Culture | Korean language | Korea-related topics | Free |
| Encyclopedia Sindhiana | Sindhi language | General interest regarding Sindh | Limited free access and features |
| Internet Encyclopedia of Ukraine | English | Ukraine, its history, people, geography, society, economy, and cultural heritage, based on the five-volume print Encyclopedia of Ukraine | Free |
| Gazetteer for Scotland | English | Articles on the geography and locations of Scotland | Free |
| Historical Dictionary of Switzerland | French, German and Italian | Articles on the history of Switzerland. | Free (without illustrations) |
| Kodansha Encyclopedia of Japan | English | Comprehensive articles on , culture, history, and politics, etc. | Subscription |
| Oslo byleksikon | Bokmål (Norwegian) | Online encyclopedia of Oslo, operated by the Society for Oslo Byes Vel, with an emphasis on places, buildings and historical events. | Free |
| Panyathai | Thai language, limited English | General interest. Designed to honor the Thai king Bhumibol Adulyadej | Free |
| Sahapedia | English | Open encyclopedic resource on the arts, cultures, and histories of India." About Us." Sahapedia. Retrieved March 1, 2021. | Free |
| English, Māori | Site operated by the New Zealand government regarding information about the country | Free | |
| Vienna History Wiki | German | Articles on the history of the city of Vienna. Includes 31,000 entries from the 2nd edition of Historisches Lexikon Wien. | Free |
| Turkpidya | English, German, Danish, Spanish, French, Italian, Hungarian, Dutch, Portuguese, Romanian, Turkish, Croatian, Polish, Czech, Greek, Bulgarian, Russian, Serbian, Hebrew, Arabic, Persian, Japanese, and Korean. | Online encyclopedia about Turkey and Turkic peoples | Free |
| Unam Wiki | Korean | Wiki with stated South Korean conservative leanings. | Free |
| 64 Parishes | English | Online encyclopedia of Louisiana, run by the Louisiana Endowment for the Humanities. | Free |
| Encyclopedia of Alabama | English | Encyclopedia covering the state of Alabama, sponsored by the Alabama Humanities Foundation. | Free |
| Encyclopedia of Appalachia | English | Dedicated to the region, people, culture, history, and geography of Appalachia. | Defunct |
| Encyclopedia of Arkansas | English | Project of the Central Arkansas Library System and is the only U.S. state encyclopedia sponsored by a public library | Free |
| Encyclopedia of Chicago | English | Free | |
| Encyclopedia Virginia | English | Encyclopedia funded by the Virginia Foundation for the Humanities and Library of Virginia, covering topics on Virginia | Free |
| Handbook of Texas | English | Articles on the U.S. State of Texas | Free |
| HistoryLink | English | Articles about Washington state history | Free |
| MNopedia | English | Online encyclopedia about Minnesota, published by the Minnesota Historical Society. | Free |
| NCPedia | English | Encyclopedia coordinated and managed by the North Carolina Government and State Library of North Carolina, covering a broad spectrum of topics and resources about North Carolina. | Free |
| New Georgia Encyclopedia | English | Articles on the U.S. state Georgia | Free |
| The Oregon Encyclopedia | English | Articles about Oregon | Free |
| Tennessee Encyclopedia | English | Covers the state of Tennessee | Free |
| Don Markstein's Toonopedia | English | Focuses on articles about print and animated cartoons | Free |
| The Encyclopedia of Science Fiction | English | Authors, books, films of sci-fi. | Free |
| Emojipedia | English | Emoji | Free |
| Fringepedia | English | Contains articles about the American television drama Fringe. | Free |
| h2g2 | English | Collection of sometimes humorous encyclopedia articles, based on Douglas Adams's The Hitchhiker's Guide to the Galaxy. | Free |
| Heroes Wiki | English, Dutch language, French, German, Hebrew language, Italian, Portuguese, Spanish, Swedish language, Turkish language | Contains articles pertaining to the American television drama Heroes. | Free |
| Know Your Meme | English | A website and video series which uses wiki software to document various and other online phenomena, such as , , , and internet celebrities. | Free |
| Lostpedia | English, German, Spanish, French, Italian, Japanese, Dutch language, Polish language, Portuguese, Russian, Chinese | Contains articles pertaining to the hit drama Lost | Free |
| Memory Alpha | English, Bulgarian, Catalan language, Czech language, German, Esperanto, Spanish, French, Italian language, Japanese, Dutch language, Polish language, Portuguese, Romanian, Russian, Serbian language, Swedish language, Ukrainian, Chinese | Articles about Star Trek | Free |
| Minecraft Wiki | English language, Russian language, Chinese language, Portuguese, Japanese, German language, French language, Spanish language, Ukrainian, Literary Chinese, Korean language, Polish language (unaffiliated), Dutch language, Italian language, Thai language | "Website for gathering useful information related to the Minecraft franchise". | Free |
| LyricWiki (2006–20) | Multilingual | Wiki-based lyrics database and encyclopedia | Defunct |
| Pixiv Encyclopedia | Japanese | Japanese pop-culture encyclopedia | Free |
| The Rocklopedia Fakebandica | English | Articles on fake bands from popular entertainment | Free |
| Supernatural Wiki | English | Contains articles about the American television drama Supernatural. | Free |
| Tolkien Gateway | English | J.R.R. Tolkien-related articles | Free |
| TV Tropes | English, German, Esperanto, Spanish, French, Norwegian, Finnish, Swedish, Al Bhed, Quenya | Articles related to the devices and conventions that a fiction writer can reasonably rely on as being present in the audience members' minds and expectations | Free |
| Fallout Wiki | English, German, Spanish, Bulgarian, Finnish language, French, Georgian, Hungarian, Italian, Japanese, Korean, Lithuanian, Dutch, Norwegian, Polish language, Portuguese, Russian, Swedish, Turkish language, Chinese | Fallout-related articles | Free |
| Wookieepedia | English, German, Spanish, Bulgarian, Danish language, Finnish language, French, Croatian, Hungarian, Italian, Japanese, Dutch, Norwegian, Polish language, Portuguese, Russian, Romanian, Slovak language, Slovene language, Swedish, Turkish, Chinese | Star Wars-related articles | Free |
| Wowpedia / Wowpedia | English, German, Spanish, French, Czech, Danish, Greek language, Persian language, Finnish, Hebrew language, Hungarian, Icelandic, Italian, Lithuanian, Latvian language, Dutch, Nynorsk, Bokmål, Polish, Portuguese, Brazilian Portuguese, Russian, Slovak language, Korean, Japanese, Chinese | Warcraft-related articles | Free |
| Encyclopedia of Mathematics | English | Encompasses articles on the topic of mathematics | Free |
| Encyclopedia of Triangle Centers | English | Information about ten thousands of , including coordinates, operations, incidence, , etc. | Free |
| EqWorld | English, Russian | Articles on mathematical | Free |
| MathWorld | English | Articles on a wide variety of mathematics related topics | Free |
| On-Line Encyclopedia of Integer Sequences | English | Information about hundred thousands of integer , including , related , Computer program, etc. | Free/CC BY-NC 3.0 |
| PlanetMath | English | Mathematics related topics and articles | Free/GNU |
| Stacks Project | English | A mathematics textbook writing project with the aim to cover " and the algebraic geometry needed to define them" | Free |
| nLab | English | Category theory and related topics | Free |
| Bulgarian Rock Archives | Bulgarian | Archives of Bulgarian rock music bands. | Free |
| Canadian Pop Music Encyclopedia | English | Encyclopedia of Canadian pop music | Free |
| Encyclopaedia Metallum | English | Archives of heavy music bands | Free |
| Grove Music Online | English | Mostly on historic and classical music worldwide. It is the online version of The New Grove Dictionary of Music and Musicians, which has 20 printed volumes and was first published in 1980. | Subscription |
| IMDb | English, German, French, Hungarian, Italian, Polish, Portuguese, Romanian, Turkish, and Spanish | Information related to world , television programs, , , and internet Streaming media | Free |
| Liquipedia | English, Russian, German, French, Dutch, Swedish | Covers esports in over sixty different games | Free |
| MusicBrainz | English, German, French, Italian, Dutch | An open music encyclopedia that collects music metadata. | Free |
| MOOMA | Hebrew language | Articles on Israeli music and musical artists | Free |
| PCGamingWiki | English | Covers PC game | Free |
| Prog Archives | English | Archives of progressive rock bands | Free |
| Rate Your Music | English | Online encyclopedia of music releases | Free |
| Rock in China | English | Documents and archives contemporary Chinese music, ranging from Chinese rock to Chinese punk, Chinese metal, electro, jazz and hip-hop | Free |
| Internet Encyclopedia of Philosophy | English | Philosophy related articles | Free |
| Marxists Internet Archive | Multilingualism | Topics related to the study of Marxism | Free |
| RationalWiki | English | Skeptical interests | Free |
| Routledge Encyclopedia of Philosophy | English | Philosophy articles | |
| Stanford Encyclopedia of Philosophy | English | Philosophy subjects | Free |
| Ballotpedia | English | American politics, elections, and public policy | Free |
| The Concise Encyclopedia of Economics | English | Economics – part of the Library of Economics and Liberty. Edited by David R. Henderson | Free |
| Cyclopaedia of Political Science, Political Economy, and the Political History of the United States | English | Articles about science, economics, and American authors. The 1899 edition is available online | Free |
| Diplopedia | English | US State Department internal encyclopedic wiki, available for diplomats and overseas US agents to use | Access only through the State Department |
| dKosopedia | English | Political encyclopedia written from a progressive/liberal Democratic point of view | Free |
| Encyclopedia Titanica | English | Encyclopedia related to the building and sinking of the RMS Titanic | Free |
| Encyclopedia of World Problems and Human Potential | English | Presents articles on perceived human problems | Free |
| Gapminder | English | Historical global trends in health, poverty, and demographics | Free |
| glbtq.com | English | Gay, lesbian, bisexual, transgender, and queer culture. | Free |
| HistoryLink | English | Articles on the history of Washington state | Free |
| Holocaust Encyclopedia | English, Arabic language, Persian language, French, Spanish | Holocaust-related articles, published by the United States Holocaust Memorial Museum | Free |
| JurisPedia | Arabic language, English, Chinese, French, German, Spanish, Dutch language | An academic encyclopedia on the concepts of law | Free |
| Max Planck Encyclopedia of Public International Law | English | Encyclopedia on public International Law | Free |
| Online Encyclopedia of Mass Violence | French | Electronic database focusing on and of the 20th century. The Online Encyclopedia of Mass Violence. Retrieved March 1, 2021. Archived. | Free |
| Our World in Data | English | Global trends on economic growth, poverty, health, war, violence, education, and demographics | Free |
| Spartacus Educational | English | Free | |
| World History Encyclopedia | English | The world's most-read history encyclopedia, covering world history from all time periods; reviewed by an editorial team, not a Wiki. | Free |
| AhmadiPedia | English | Dedicated to the study of the Worldwide Ahmadiyya Muslim Community. | Free, public domain |
| Catholic Encyclopedia | English | Topics relating to Catholicism, text from 1913 and 1922 | Free, public domain |
| Christian Cyclopedia | English | Collection of historical and theological information | Free |
| Easton's Bible Dictionary | English | Articles on Christianity and theology | Free, public domain |
| Encyclopaedia Biblica | English | Contains articles about "the Literary, Political and Religious History, the Archaeology, Geography, and Natural History of the Bible" | Free |
| Encyclopedia of Mormonism | English | Articles by Mormon studies on history and doctrine of the Church of Jesus Christ of Latter-day Saints (LDS Church). | Free |
| Global Anabaptist Mennonite Encyclopedia Online | English | Topics relating to Anabaptism and | Free |
| Halachipedia | English | Topics relating to Halakha. | Free |
| İslâm Ansiklopedisi | Turkish language | Articles on topics concerning Islamic studies. | Free |
| The Jewish Encyclopedia | English | Topics relating to Judaism | Free |
| Jewish Virtual Library | English | Portals to essential Jewish topics | Free |
| Encyclopedia Mythica | English | Covers folklore, mythology, and religion. | Free |
| Punjabipedia | Punjabi language | Entries on Sikhism | Subscription |
| Schaff–Herzog Encyclopedia of Religious Knowledge | English | Christian, published 1908–1914 | Free, public domain |
| WikiShia | Various | Shia Islam, published since 2013 | Free |
| Encyclopedia Astronautica | English | Contains articles on the subject of space exploration and astronomy, no longer updated since 2019 | Free |
| Encyclopedia of Earth | English | Articles on the Earth and its ecosystems | Free |
| Engineering and Technology History Wiki | English | The history of technology, a partnership between the United Engineering Foundation, and the AIChE, AIME, ASCE, ASME, IEEE, SPE, and SWE | Free |
| Free On-line Dictionary of Computing | English | Computing and related subjects | Free |
| Glottopedia | English | Linguistics | Free |
| Javapedia | English | Coverage of all topics related to the Java Platform | Free |
| Omniglot | English | Covers languages and writing systems. | Free |
| Proteopedia | English | Wiki-based 3D encyclopedia of and other . | Free |
| RP Photonics Encyclopedia | English | Laser technology, photonics, and various other areas of photonics such as nonlinear optics, non-laser light sources, fiber optics, and of light. | Free |
| ScienceWorld | English | Covers astronomy, scientific biography, chemistry, and physics. Like MathWorld, it is edited by Eric Weisstein. | Free |
| Animal Diversity Web | English | Student wiki-type database at the University of Michigan of animal natural history, distribution, classification, and conservation biology. | Free |
| APpedia | Chinese | Contains articles on the subject of general animal rights | Free |
| ARKive | English | Visual and audio recordings of the world's species | Defunct |
| Encyclopedia of Life | English, French | Seeks to categorize all 1.8 million known species on the planet | Free |
| Encyclopedia of Life Sciences | English | Biology related articles | Subscription |
| Encyclopedia of Life Support Systems | English | Articles about the Natural science and social sciences | Subscription |
| Erowid | English | Information about psychoactives substances | Free |
| FishBase | English, Spanish, Portuguese, French, German, Italian, Dutch language, Chinese (Simplified Han), Chinese (Traditional Han), Greek language, Swedish language, Russian, Persian language, Vietnamese, Thai language, Lao language, Hindi, Bengali language | Articles on fish species | Free |
| Flora Europaea | English | Covers different plant species | Free |
| King Abdullah Bin Abdulaziz Arabic Health Encyclopedia | Arabic language, English | Health encyclopedia | Free |
| Palaeos | English | Covers palaeontology | Free |
| World Flora Online | English | Covers the world's plant species | Free |
| Wikispecies | English | Seeks to create a catalog of all living things | Free |
| ZipcodeZoo | English | Encyclopedia of all living things | Defunct |
| Ganfyd | English | Online medical wiki | Defunct |
| Radiopaedia | English | Articles on medical imaging used in radiology and radiography | Free |
| WikEM | English | An emergency medicine open-access source | Free |
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