BitThief
BitThief is an ongoing project of the Distributed Computing Group at ETH Zurich. The project deals with incentive problems in peer-to-peer filesharing systems.
The sources in this project are current as of January 2007 when I stopped coding on the project as part of my Master Thesis. ETH has since improved the client and the latest version (closed source) will always be available at http://bitthief.ethz.ch/.
BitThief is a byproduct of our HotNets-V paper "Free Riding in BitTorrent is Cheap" (http://www.disco.ethz.ch/publications/hotnets06.pdf).