KOReader

An ebook reader application supporting PDF, DjVu, EPUB, FB2 and many more formats, running on Cervantes, Kindle, Kobo, PocketBook and Android devices portable: runs on embedded devices (Cervantes, Kindle, Kobo, PocketBook, reMarkable), Android and Linux computers. Developers can run a KOReader emulator in Linux and MacOS.

multi-format documents: supports fixed page formats (PDF, DjVu, CBT, CBZ) and reflowable e-book formats (EPUB, FB2, Mobi, DOC, RTF, HTML, CHM, TXT). Scanned PDF/DjVu documents can also be reflowed with the built-in K2pdfopt library. ZIP files are also supported for some formats.

full-featured reading: multi-lingual user interface with a highly customizable reader view and many typesetting options. You can set arbitrary page margins, override line spacing and choose external fonts and styles. It has multi-lingual hyphenation dictionaries bundled into the application.

integrated with calibre (search metadata, receive ebooks wirelessly, browse library via OPDS), Wallabag, Wikipedia, Google Translate and other content providers.

optimized for e-ink devices: custom UI without animation, with paginated menus, adjustable text contrast, and easy zoom to fit content or page in paged media.

extensible: via plugins

fast: on some older devices, it has been measured to have less than half the page-turn delay as the built in reading software.

and much more: look up words with StarDict dictionaries / Wikipedia, add your own online OPDS catalogs and RSS feeds, over-the-air software updates, an FTP client, an SSH server, …