Check it out here: http://www.bookupapp.com/
App Store link: https://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=1104416604
Available for iPhone and iPad. Android version coming shortly – check back!
The Bookup App is for readers of print books who want to swap their books for other books in their area, free of charge, and potentially make a new friend with a shared interest in reading. Bookup provides location-based book swapping functionality. Has your library of print books been building up over the years? Taking used books to a bookstore and reselling them is often impossible – bookstores just aren't interested.
If you don't reread your books often, then they just end up gathering dust on a bookshelf. Why not give these books of yours a new life by "hooking them up" with a new owner in your geographic area?