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,
Easy Ebook Viewer - A Simple Reader for ePub Files on Linux
GitHub - lrusso/TinyEPUBReader: Tiny EPUB Reader developed in JavaScript
GitHub - koreader/koreader: An ebook reader application supporting PDF, DjVu, EPUB, FB2 and many more formats, running on Cervantes, Kindle, Kobo, PocketBook and Android devices