Peer to peer sharing of physical books.
A book sharing app for local communities like a college; hard copy of books not digital.
You scan a book's bar code, add it your profile, mark it as available to lend. Somebody can borrow, you can keep track of it (no loosing books any more, trying to recall who borrowed what :-)
Other benefit is that some books are not easily available to order, but are sometimes just around us.
Currently work in progress on a Django based web app. Plans to provide a Android app frontend as well.