Last December, someone pointed me to Matriux. In their own words:
It is a fully featured security distribution consisting of a bunch of powerful, open source and free tools that can be used for various purposes including, but not limited to, penetration testing, ethical hacking, system and network administration, cyber forensics investigations, security testing, vulnerability analysis, and much more. It is a distribution designed for security enthusiasts and professionals, although it can be used normally as your default desktop system.
It comes with a wide arsenal of free software tools to do naughty things to your network. I think I should give it a swing and download it some time.
I wonder how it compares to Backtrack. I’m told that Backtrack includes a lot of proprietary stuff, like firmwares, to be able to do passive scanning on certain network cards. Matriux is purely open source, so things like that would be impossible.