StepMania
Think of this as an introductory post into something I may mention more in the future. This way I can just send people here instead of explaining everything from scratch every time :P
Ever heard of Dance Dance Revolution (Dancing Stage in Europe)? Well it’s a funky arcade game you control by “dancing”. Arrows scroll up the screen and when they reach the top you press the corresponding button.
The really cool thing is a an open source PC version of it called StepMania. Generally StepMania has more features and allows you to add as many songs as you want (assuming you can get the media files and step charts). In fact there are arcade machines around that are actually a computer running StepMania inside a DDR cabinet (which is a little overwhelming to play because of the sheer number of songs available.