Many DDR players opt to use StepMania to help them practice their sight reading of notes, to familiarize themselves with songs or just to quell the cravings that a winter break without DDR can cause. Others get a USB adapter to go with their dance pad and play StepMania as it was meant to be played. Or one can get songs that are physically impossible to do on feet and attempt to break the sound barrier with their fingers.
The CLoA of (keyboard) StepMania is often very different from that in DanceDanceRevolution, primarily due to the fact that it doesn't require a lot of physical motion, so stamina doesn't come into play.
StepMania can be downloaded [here], while song files can be procured at [DDR:UK], unless it's down. Files are also available on the Mudd network for on-campus folk. Also, [Bemanistyle] has song files, although they're all homemade (none of the "real" DDR songs), so the quality of the steps varies.
StepMania can be rather resource-hungry, causing songs to skip or sound burbly. This is why SeleneTan uses DanceWithIntensity? instead, which is similar but less resource-hungry, although also not open source. The problem could be solved with a framerate throttle -- it's what solved the same problem in DanceWithIntensity?. "Drawing" twice as many frames as the monitor's refresh rate is... umm... wasteful. And takes up all my CPU cycles, leaving none for minor things like playing sounds or decoding MP3s...
And you people using DDR simulators had better try doing two-handed versus with different difficulties for the two hands. Different key layouts optional. My high score (more like CLoA) looks lonely.