wut...is that?...neverherd o it...
It's a Dance Dance Revolution (You know, the arcade game where you stand on a metal platform and step on the arrows with your feet as the arrows go by on the screen) simulator for PC. You download it for free, and then you can download whatever song packs you want from the internet to use, and you can even program your own songs with dance steps and everything. Totally customizable. To simulate the footsteps, you can use your keyboard, or what's really cool is that you can use your own dance mat so its just like real DDR. I already had a dance mat for the Xbox version of DDR, so I just bought the Xbox to PC converter and I was all set to go! It really is very awesome.
Oops, I kind of went overboard in the explaining. Sorry about that! ^^;