Best Open-Source Ebook Readers 2026: 6 Options Compared
Best open-source Ebook Readers compared: calibre, KOReader, Foliate, Thorium Reader and 2 more, with licenses, platforms and prices from official pages checked October 24, 2026.
•3 min read•Learning & Everyday Apps
Quick comparison
| Tool | Price | Platforms | Best for | Tested |
|---|---|---|---|---|
| calibre | Free (Free and open source e-book manager and converter) | Desktop | Managing a large library | Docs only |
| KOReader | Free (Free open-source document reader for e-ink devices, Android and desktop) | Android, Kindle, Kobo, PocketBook, Linux, macOS | E-ink readers and PDFs | Docs only |
| Foliate | Free (Free open-source GTK ebook reader for Linux) | Linux | Linux desktop reading | Docs only |
| Thorium Reader | Free (Free open-source desktop reading app for EPUB, PDF and audiobooks) | Windows, macOS, Linux | Accessible reading on desktop | Docs only |
| Readest | Free (The reader's source code is AGPL-3.0; the project also offers a hosted sync service whose terms were not checked) | Windows, macOS, Linux, Android, iOS, Web browser | Reading across phone and laptop | Docs only |
| Koodo Reader | Free (Source code is AGPL-3.0; the project also sells a Pro version whose price was not checked) | Windows, macOS, Linux, Web browser, Android, iOS | A single app on every platform | Docs only |
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Good fit if
- You read on a Kobo or Kindle and want control (KOReader is the pick)
- You need to convert or organize hundreds of books (calibre is the pick)
- You use Linux desktop and want a tidy reader (Foliate is the pick)
- You need accessible reading tools (Thorium Reader is the pick)
Not ideal if
- You cannot host, patch and back up a server yourself and want a vendor to run it
An open-source ebook reader gives you a way to read EPUB and PDF files without a store account tied to the device. The main decision is where you read. KOReader targets e-ink devices such as Kindle, Kobo and PocketBook as well as Android and desktop, and it handles PDF reflow better than most. Calibre is a library manager and converter first, so it suits anyone moving files between formats or devices, but its reading view is plain. Foliate is a clean GNOME reader for Linux, Thorium Reader supports EPUB, PDF and audiobooks on Windows, macOS and Linux, and Readest and Koodo Reader add sync and Android or iOS apps. Licensing differs: most of these are GPL or AGPL, Thorium is BSD-3-Clause, and a few projects sell optional cloud sync or a Pro tier; check each project for current pricing. None of them can open store-protected files, so books bought with copy protection need DRM removal that these projects do not provide. Think about syncing too, because progress and highlights are the features that move between devices and the ones free tools handle least evenly.
calibre
GPL-3.0 library manager, converter and reader for Windows, macOS and Linux. Best for organizing and converting, less pleasant for reading.
Price: Free (Free and open source e-book manager and converter) (calibre pricing, checked 2026-10-24).
Platforms and license: Desktop. GPL-3.0 (open source) (license source).
Project activity: 26.3k GitHub stars · latest release v9.17.0 (Oct 23, 2026) · last commit Oct 27, 2026
Best for: Managing a large library.
Worth knowing: Whether a given PDF converts cleanly was not tested. License taken from the repository metadata and LICENSE file; description from the project README. No paid plan was checked.
KOReader
AGPL-3.0 reader that runs on e-ink devices, Android and desktop, with strong PDF handling and many customization options.
Price: Free (Free open-source document reader for e-ink devices, Android and desktop) (KOReader pricing, checked 2026-10-24).
Platforms and license: Android, Kindle, Kobo, PocketBook, Linux, macOS. AGPL-3.0 (open source) (license source).
Project activity: 30.7k GitHub stars · latest release v2026.07.1 (Aug 1, 2026) · last commit Oct 27, 2026
Best for: E-ink readers and PDFs.
Worth knowing: License verified from the repository LICENSE/COPYING file on GitHub on 2026-10-24; platforms listed from project knowledge, not re-verified on the project site.
Foliate
GPL-3.0 GTK reader for Linux with annotations and a clean interface. Linux only, so Windows and Mac users must look elsewhere.
Price: Free (Free open-source GTK ebook reader for Linux) (Foliate pricing, checked 2026-10-24).
Platforms and license: Linux. GPL-3.0 (open source) (license source).
Project activity: 8.8k GitHub stars · latest release 3.3.0 (Apr 1, 2025) · last commit Apr 8, 2026
Best for: Linux desktop reading.
Worth knowing: License verified from the repository LICENSE/COPYING file on GitHub on 2026-10-24; platforms listed from project knowledge, not re-verified on the project site.
Thorium Reader
BSD-3-Clause desktop app for EPUB, PDF and audiobooks, built on Readium and supporting accessibility features. No mobile apps.
Price: Free (Free open-source desktop reading app for EPUB, PDF and audiobooks) (Thorium Reader pricing, checked 2026-10-24).
Platforms and license: Windows, macOS, Linux. BSD-3-Clause (open source) (license source).
Project activity: 2.9k GitHub stars · latest release v3.5.1 (Sep 2, 2026) · last commit Oct 27, 2026
Best for: Accessible reading on desktop.
Worth knowing: License verified from the repository LICENSE/COPYING file on GitHub on 2026-10-24; platforms listed from project knowledge, not re-verified on the project site.
Readest
AGPL-3.0 reader for desktop, mobile and web with sync. A hosted sync service exists; check its terms before using it.
Price: Free (The reader's source code is AGPL-3.0; the project also offers a hosted sync service whose terms were not checked) (Readest pricing, checked 2026-10-24).
Platforms and license: Windows, macOS, Linux, Android, iOS, Web browser. AGPL-3.0 (open source) (license source).
Project activity: 25.7k GitHub stars · latest release v0.12.16 (Oct 13, 2026) · last commit Oct 27, 2026
Best for: Reading across phone and laptop.
Koodo Reader
AGPL-3.0 reader for desktop, web and mobile. The project also sells a Pro version; check the project for current pricing.
Price: Free (Source code is AGPL-3.0; the project also sells a Pro version whose price was not checked) (Koodo Reader pricing, checked 2026-10-24).
Platforms and license: Windows, macOS, Linux, Web browser, Android, iOS. AGPL-3.0 (open source) (license source).
Project activity: 28.6k GitHub stars · latest release v2.4.6 (Oct 7, 2026) · last commit Oct 27, 2026
Best for: A single app on every platform.
Which one to pick
- You read on a Kobo or Kindle and want control: KOReader
- You need to convert or organize hundreds of books: calibre
- You use Linux desktop and want a tidy reader: Foliate
- You need accessible reading tools: Thorium Reader
Limits of this review
Docs-only for calibre, KOReader, Foliate, Thorium Reader, Readest, Koodo Reader: we did not install or run them, so feature claims come from vendor pages. Vendor prices and free limits change; confirm on the linked pricing page before you commit.
Related guides
Sources
Kevin Fan
Kevin Fan is a SaaS founder. He runs Free Instead Of, which tracks free and open-source alternatives to paid software and checks each price and free-plan limit against the vendor's own pages.
Methodology
Based on official pricing, license and product pages checked 2026-10-24: calibre, KOReader, Foliate, Thorium Reader, Readest, Koodo Reader. Prices, free limits and licenses are the figures shown on those pages on those dates. No tool on this page was installed or run. No accounts were created.