Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
calibre - Ebook manager, viewer & converter
PDFZen - The powerful, simple, free online PDF editor for the masses; free yourself from the fax machine!
FBReader - FBReader is an e-book reader for various platforms. Features:
Xodo - Try easy-to-use PDF tools that keep your documents safe. Work with your important files across all platforms and devices with the ultimate all-in-one document solution. Your productivity lives at Xodo!
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.