calibre - Ebook manager, viewer & converter
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Calibre Web - Calibre Web is a web app providing a clean interface for browsing, reading and downloading eBooks...
FBReader - FBReader is an e-book reader for various platforms. Features:
Okular - Okular is a universal document viewer based developed by KDE.
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices