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Orion Viewer vs Episteme Reader: catalog facts
Orion Viewer	Episteme Reader
Free Free and open source under the GPL.	Free Free and open source under the AGPL-3.0.
Android	Android, iOS
Opens DjVu as well as PDF, XPS, CBZ and TIFF Configurable tap zones and key bindings for page turning	Reads PDF, EPUB, MOBI and AZW3 in one app Also opens Markdown, HTML and plain text
Viewer only, with no PDF editing Interface is functional rather than polished	Desktop and iOS versions are not confirmed as released Contributions require signing a CLA
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0-or-later	License: AGPL-3.0
No account needed	Not stated if an account is 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.