Calibre is a ‘free and open source e-book library management application developed by users of e-books for users of e-books. It has a cornucopia of features divided into the following main categories: library management; e-book conversion; syncing to e-book reader devices; downloading news from the web and converting it into e-book form; comprehensive e-book viewer; content server for online access to your book collection.’
Recently I bought a Kobo eReader and desperately needed software to manage my ebooks, as well as converting documents to the ePub format to read on the device. Calibre does all this and more. Not only does Calibre provide easy tools for library management (getting books on and off the Kobo is a dream via Calibre) but it connects to the web to get the latest metadata including cover images. Converting a book to epub format is painless as is adding/editing metadata. The ability to download local and world news is brilliant.
Calibre comes in three flavours (Windows, Mac and Linux) and its open source community seems active, ensuring the latest eReaders are supported.