What are some alternatives?
Amazon Kindle - Amazon Kindle software lets you read ebooks on your Kindle, iPhone, iPad, PC, Mac, BlackBerry, and...
calibre - Ebook manager, viewer & converter
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices
iBooks - iBooks is an amazing way to download and read books.
Project Gutenberg - Project Gutenberg offers free ebooks to download.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.