Vipul's Razor is an
opensource package for collective detection and marking of
spam so that it can be
filtered by end-users. Special
algorithms are used to detect slightly modified versions of the same spam and the integrity of the system is upheld by skewing results towards reports submitted by users with a better reputation. Reputation is gained by accurately submitting spam.
The project is hosted by sourceforge and gets it name from the package's author, Vipul Ved Prakash. It is freely available under the artistic license