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