Calibre is an Ebook management software.

FBReader is a free ebook reader. Main ebook formats: ePub (including main features of ePub3), Kindle azw3 (mobipocket), fb2(.zip).

Cool Reader is a configurable eBook viewer.

Okular is a universal document viewer based developed by KDE.

Sigil is a free, open source, multi-platform ebook editor.

EPUB is an e-book file format with the extension .epub that can be downloaded and read on devices like smartphones, tablets, computers, or e-readers.