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KOReader vs FBReader: catalog facts
KOReader	FBReader
Free Free and open source under the AGPL 3.0.	Freemium The reader is free. Some format plugins and premium features are paid.
Linux, Android	Windows, macOS, Linux, Android, iOS
Runs on Kindle, Kobo, PocketBook, Cervantes and reMarkable hardware Opens PDF, DjVu, CBZ, EPUB, FB2, Mobi, DOC, RTF, HTML, CHM and TXT	Same library and reading position across desktop and mobile Reads custom OPDS catalogues as well as local files
Installing on a locked e-reader means jailbreaking it first, at your own risk The settings menus are deep and not self-explanatory	Some features and formats need paid add-ons The desktop builds lag the mobile apps
Downloadable app	Downloadable app
Open source	Closed source
License: AGPL-3.0	License not stated
No account needed	Not stated if an account is needed
Works offline	Not stated if it works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked September 22, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.