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Calibre vs Thorium Reader: catalog facts
Calibre	Thorium Reader
Free Free and open source, funded by donations.	Free The open-source software is available without a license fee. Hosting, hardware and…
Windows, macOS, Linux	Windows, macOS, Linux
Converts between all the major ebook formats, including for Kindle Fetches metadata and covers from the internet automatically	Supports library imports, bookmarks and adjustable reading layouts.
The interface is dense and has accumulated two decades of features It will not remove DRM; that requires third-party plug-ins with their own legal questions	Format and protection support depend on the book being opened.
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: BSD-3-Clause
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 20, 2026	Official website Full listing and sources Checked September 22, 2026

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