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Thorium Reader vs FBReader: catalog facts
Thorium Reader	FBReader
Free The open-source software is available without a license fee. Hosting, hardware and…	Freemium The reader is free. Some format plugins and premium features are paid.
Windows, macOS, Linux	Windows, macOS, Linux, Android, iOS
Supports library imports, bookmarks and adjustable reading layouts.	Same library and reading position across desktop and mobile Reads custom OPDS catalogues as well as local files
Format and protection support depend on the book being opened.	Some features and formats need paid add-ons The desktop builds lag the mobile apps
Downloadable app	Downloadable app
Open source	Closed source
License: BSD-3-Clause	License not stated
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 September 22, 2026

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