What are some alternatives?
When comparing FBReader and calibre, you can also consider the following products
Amazon Kindle - Amazon Kindle software lets you read ebooks on your Kindle, iPhone, iPad, PC, Mac, BlackBerry, and...
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Adobe Digital Editions - ebook reader software
Document Viewer - Document Viewer is a highly customizable document viewer for Android. - SufficientlySecure/document-viewer