CoolReader vs FBReader

Free open-source, XML/CSS-based e-book reader for Windows and Linux. There's also mobile version for Android and some eInk devices. Supported formats include FB2, TXT, RTF, DOC, TCR, HTML, EPUB, CHM, PDB, and MOBI. The program offers numerous settings for improved reading experience. It's arguably the best reader for Linux, but on Windows, it has some issues, such as linking e-book extensions to the program so it opens when clicking on a book file.

Free e-book reader that supports multiple file formats, including ePub, fb2, mobi, HTML, RTF, HTML, plain text, doc, and more. FBReader uses its own page parsing and rendering engine - very lightweight, fast and customizable. It supports embedded images, footnotes, hyperlinks, text search, full-screen reading. It also automatically creates bookmarks so you don't lose track of where you left off after closing a book. It works on iOS, Android, Windows, Mac OS, Linux, and Chrome OS. Books can be synced across devices or stored in Google Drive. For Android and iOS there are both free and paid versions. Free versions have some limitations.