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FBReader vs Librum: catalog facts
FBReader	Librum
Freemium The reader is free. Some format plugins and premium features are paid.	Free Free and open source.
Windows, macOS, Linux, Android, iOS	Windows, macOS, Linux
Same library and reading position across desktop and mobile Reads custom OPDS catalogues as well as local files	Reader and library manager in one app Runs on several desktop platforms
Some features and formats need paid add-ons The desktop builds lag the mobile apps	Sync depends on the project's service Smaller project than established readers like Calibre
Downloadable app	Downloadable app
Closed source	Open source
License not stated	License: GPL-3.0
Not stated if an account is needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked October 2, 2026

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