KOReader
FreeInstall it on a Kindle or e-ink device and take the reader back
An open-source reader designed for e-ink devices, handling EPUB, PDF, DJVU, comics and more. It installs onto Kindle, Kobo, Onyx Boox and PocketBook hardware, and an Android build exists too. Typography control is unusually fine-grained, with PDF reflow, dictionary lookup, translation and reading statistics.
Why we picked it
Stock firmware on e-readers usually has three problems: limited format support (Kindle long refused EPUB), a home screen selling you books, and reading data reported back to the vendor. The hardware itself is generally excellent.
KOReader liberates that hardware. 28,983 stars, AGPL-3.0, installable on Kindle, Kobo, Onyx Boox and PocketBook devices, with Android and Linux desktop builds as well.
Its most praised quality is granular typography control, which matters enormously on e-ink:
- Font, size, line spacing, letter spacing, paragraph spacing and margins are all adjustable as continuous values rather than a handful of presets.
- Embedded and custom fonts are supported, so you can choose typefaces that suit your language.
- PDF reflow is the killer feature. A two-column academic paper is unreadable on a six-inch screen; KOReader reflows the text into a single column sized for the display.
- Partial and full e-ink refresh behavior can be tuned per device to reduce ghosting.
Reading aids are thorough: a built-in dictionary (importable StarDict dictionaries), lookup translation, highlights and annotations, bookmarks, cross-device progress sync with a self-hostable sync server, and detailed statistics on time read, average speed and per-book progress.
Format coverage far exceeds stock firmware: EPUB, PDF, DJVU, MOBI, FB2, CBZ/CBR comics, TXT and CHM.
To be clear about:
- Installation takes effort. Kindle requires jailbreaking first; Kobo is comparatively simple; the Android APK is the easiest path. Jailbreaking carries risk — community guides are mature and the process is usually reversible, but assess it yourself, weighing warranty and the possibility of bricking the device.
- The interface is plain. It is function-driven, with deep menus and an overwhelming number of options. Defaults are readable, and the advanced settings can wait.
- It is not a library manager. Organizing hundreds of books, converting formats and fetching metadata remain Calibre's job; transfer the results to the device for KOReader to read.
If you own an e-ink device and are unhappy with its stock reading experience, this is essentially the only and the best answer. For reading only on a computer, see Thorium Reader.