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
FBReader - FBReader is an e-book reader for various platforms. Features:
Moon Reader - Innovative book reader with powerful controls & full functions
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.