calibre - Ebook manager, viewer & converter
OpenAudible - OpenAudible Project Page
Convertio - File Conversion in the Cloud
RoxyApps eBook Conversion Tool - Convert djvu, epub, fb2, lit, azw, lrf and other eBook files to txt, pdf, pdb, rtf and other formats
CBconvert - A comic book converter with support for .cb*, .pdf, .xps, .epub, .mobi and directories.
TunesKit iBook Copy for Mac - Easily remove DRM protection from Apple iBooks and copy DRM protected iBooks to DRM free ePub files.