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Calibre vs Librum: catalog facts
Calibre	Librum
Free Free and open source, funded by donations.	Free Free and open source.
Windows, macOS, Linux	Windows, macOS, Linux
Converts between all the major ebook formats, including for Kindle Fetches metadata and covers from the internet automatically	Reader and library manager in one app Runs on several desktop platforms
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	Sync depends on the project's service Smaller project than established readers like Calibre
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: GPL-3.0
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 October 2, 2026

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