Is your e-book collection is a disorganised mess of different formats and competing viewers? It doesn't have to be that way. Calibre is an e-book management tool that will quickly bring order to the situation, and help you get more from the format, and (if you have one) your portable e-book reader.
The process starts by letting the program organise your e-books library. Point calibre at your files and it'll quickly (and almost automatically) build a database around your collection, downloading metadata like covers for extra visual appeal. You can then sort and search your books by title, author, date published, rating, custom tags and more, making it quick and easy to find whatever you need.
Calibre can then display your book, too (as long as it's not DRM-protected), with an integrated viewer that handles all the main formats and supports features like table of contents, CSS, printing, searching, embedded fonts and more.
You also get a comprehensive conversion tool that will convert documents in all the main e-book formats (CBZ, CBR, CBC, EPUB, FB2, HTML, LIT, LRF, MOBI, ODT, PDF, PRC, PDB, PML, RB, RTF, TCR, TXT) to any of twelve standard formats (EPUB, FB2, OEB, LIT, LRF, MOBI, PDB, PML, RB, PDF, TCR, TXT).
And there are many surprising extras. Calibre can automatically fetch news from websites or RSS feeds, for instance, then format the results into an eBook. A powerful sync tool will work with many different devices, from dedicated e-book readers like the Kindle to Android phones and the iPhone. And the program even includes an integrated web server that allows you to access your e-book collection from a browser, anywhere in the world.
Note this is the portable version of Calibre.