Nemesis: A Packet Injection Utility

"Nemesis is a command-line network packet injection utility for UNIX-like and Windows systems. You might think of it as an EZ-bake packet oven or a manually controlled IP stack. With Nemesis, it is possible to generate and transmit packets from the command line or from within a shell script. Nemesis attacks directed through fragrouter could be a most powerful combination for the system auditor to find security problems that could then be reported to the vendor(s)." read more...

Website: http://www.packetfactory.net/projects/nemesis