calibre is an e-book library manager. It can view, convert and catalog e-books in most of the major e-book formats. It can also talk to e-book reader devices. It can go out to the internet and fetch metadata for your books. It can download newspapers and convert them into e-books for convenient reading. It is cross platform, running on Linux, Windows and OS X.
For screenshots: https://calibre-ebook.com/demo
For installation/usage instructions please see http://calibre-ebook.com
For source code access: bzr branch lp:calibre
To update your copy of the source code: bzr merge
Tarballs of the source code for each release are now available at http://code.google.com/p/calibre-ebook