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

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