YACReader
YACReader – reading, viewing and managing a collection of comics. Free and open source program
ComicReaderUltimate
ComicReaderUltimate is a program for reading comics in CBR, CBZ or JPEG format. Multiplatform free and open source program
Comic Sticks
Comic Sticks is a free and open source program for reading comics from the xkcd service for Linux
Manga Reader
Manga Reader is a free and open source program for reading manga/comics from a local library
Buka
Buka is a book manager with a simple and minimalistic user interface for organizing and reading PDF books
csBooks
csBooks – manager and reader of eBooks in PDF, EPUB and MOBI formats
Bookworm
Bookworm – free and open source software simple, focused eBook reader for Linux
Polar
Polar – free and open source cross-platform software for organizing and reading PDF files, capture web content, with support for adding annotations
Foliate
Foliate – free and open source simple and modern eBook viewer for Linux desktop
Eplee
Eplee is an ePub reader focused on reading without distraction with a simple and beautiful user interface (UI)