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Librera Reader vs Orion Viewer: catalog facts
Librera Reader	Orion Viewer
Free Free to download.	Free Free and open source under the GPL.
Android	Android
Wide format support including DjVu and comics Auto-scan of book folders with reading progress	Opens DjVu as well as PDF, XPS, CBZ and TIFF Configurable tap zones and key bindings for page turning
Android only Many settings can take time to learn	Viewer only, with no PDF editing Interface is functional rather than polished
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: GPL-3.0-or-later
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked October 2, 2026

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