FoliateA simple and modern GTK eBook reader
KoreaderAn ebook reader application supporting PDF, DjVu, EPUB, FB2 and many more formats, running on Cervantes, Kindle, Kobo, PocketBook and Android devices
Koodo ReaderA modern ebook manager and reader with sync and backup capacities for Windows, macOS, Linux and Web
bookr-mod-vitaA book reader for the Vita and Switch. Still a work in progress.
FB2LibraryCross-Platform .NET library for read .FB2 ebook files.
DotOPDSLightweight .NET OPDS server
fb2-readerEmacs plugin to read .fb2 and .fb2.zip ebooks.