THC-Hydra  

"A very fast network logon cracker which support many different services. Number one of the biggest security holes are passwords, as every password security study shows. Hydra is a parallized login cracker which supports numerous protocols to attack. This tool is a proof of concept code, to give researchers and security consultants the possibility to show how easy it would be to gain unauthorized access from remote to a system." read more...

Website: http://freeworld.thc.org/thc-hydra