Goodreads is a social network for readers that gives you the chance to rate all of the books that you've read, write reviews and, most importantly, check out recommendations from other users. This is the official Goodreads app.
You can use this app to do pretty much everything that you would on Goodreads' official website. You can rate the books you've read, look for new books using the search engine, apply genre filters, etc. And of course you can access your virtual shelves at any time.
One feature exclusive to the app allows you to use your device's camera to scan a book's barcode, which naturally gives you all of its information. Once you do it, you can add the book to your shelf, rate it, write a review, or add it to your 'to-read' list.
Goodreads is a great application for avid readers. Not only can you keep your books perfectly organized, but you can share your thoughts and recommendations with thousands of other users.