The best open source Encyclopedia alternative to Wikipedia is Kiwix. If that doesn't suit you, our users have ranked more than 50 alternatives to Wikipedia and seven of them are open source Encyclopedias so hopefully you can find a suitable replacement. Other interesting open source Encyclopedia alternatives to Wikipedia are WikiReader, Wikiless, Citizendium and WikiSpooks.com.
Provides offline access to Wikipedia and HTML content via ZIM format, featuring a full-text search engine, multi-language interface, export capabilities, bookmarks, content manager, and support for Windows, macOS, Linux, Android, USB drives, and local servers.
Supports light mode, dark mode, Material You dynamic colors and 300+ Wikipedia languages
Citizendium, powered by MediaWiki, is "an open wiki project dedicated to creating a free, comprehensive, and reliable repository of structured knowledge". Unlike with Wikipedia, a contributor must register using their real name and verify their identity.
WikiSpooks is a global alternative encyclopedia on politics, spy craft, deep state intelligence, and conspiracies, free of corporate influence, partisan politics, or government propaganda for historians and truth-seekers to read, edit, and share.
Protopedia is a wiki style database containing information on a wide array of biological macromolecules. The site offers generalized information about the molecule of interest in addition to providing 3D visuals on the structure of the molecule and information on its...
Mathematics of Reaction Networks is a website and wiki maintained and updated by an international group of researchers working in the field of Reaction Network Theory.
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It's a great tool for accessing such content offline, but not a true alternative. More of a compliment