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Orion Viewer vs Chaka Book Reader: catalog facts
Orion Viewer	Chaka Book Reader
Free Free and open source under the GPL.	Free Free and open source under AGPL-3.0-or-later.
Android	Android
Opens DjVu as well as PDF, XPS, CBZ and TIFF Configurable tap zones and key bindings for page turning	Opens a very wide range of document and comic formats Reads files directly from archives
Viewer only, with no PDF editing Interface is functional rather than polished	Android only No release downloads listed on the repository
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0-or-later	License: AGPL-3.0
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

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