calibre - Ebook manager, viewer & converter
Scribd - Unlimited books, audiobooks & comics. Unparalleled discovery. Any device. $8.99/month
FBReader - FBReader is an e-book reader for various platforms. Features:
FlippingBook - FlippingBook changes the way you present your documents
NeeView - Display two images simultaneously
Flipsnack - Flipsnack | PDF to HTML5 flipbooks