Blipoteka is an open source, web project of simple social book exchange/lending system written using PHP and Zend Framework. It powers Blipoteka.pl site — little community of people who know each other from Blip.pl (Polish Twitter counterpart) website.
For those interested: the development has been suspended for a while, but the project is not dead. However, due to the time constraints, I would be more than happy to get a helpful hand from other PHP developer. Contact me!
Update (2013-11-13): whoops, the above is no longer true — the Blip.pl service was sold to Wykop.pl and is dead now, but the community moved on and created the Blabler.pl, so there’s still a chance to revive Blipoteka (Blableroteka?…).
Download: get the sources.