FBReader

Favorite Book Reader works on computers with all major operating systems (Windows, MacOSX, Linux) and mobile devices (iOS, Android). The FBReader features are

1. Comfortable reading. Customizable text styles and colours for day and night modes, advanced navigation features, and bookmarks.
2. Configurable network book sources list, from which you can download books for free and for a fee. You also can open your local books or add your preferred OPDS catalogs. FBReader provides a powerful catalogs browser, with browsing history, bookmarks, and search.
3. Transparent cloud integration. FBReader synchronizes your books, reading positions and bookmarks across all your devices. Start reading a book on your computer, then continue from the same place on a tablet or smartphone.

Major book formats are ePub (including main features of ePub3), unencrypted Kindle azw3 (a.k.a. Mobipocket) and fb2(.zip). Other supported formats: RTF, doc (MS Word), HTML, and plain text.