GitHub - caesiumstudio/csBooks-updates: csBooks is the best epub reader, pdf reader, mobi book reader and djvu reader for windows, linux and mac os. It solves your problems if you need ebook manager,
GitHub - psiegman/epublib: a java library for reading and writing epub files
GitHub - lrusso/TinyEPUBReader: Tiny EPUB Reader developed in JavaScript
GitHub - FolioReader/FolioReaderKit: 馃摎 A Swift ePub reader and parser framework for iOS.
GitHub - wustho/epr: CLI Epub Reader
4 open source eBook readers for Android | Opensource.com