As a concept, Dance Dance Revolution is pretty simple: stomp on arrows in time with the music. And it would seem that this would be an easy concept not only to imitate and (questionably) improve, but to clone. And clone, they did.
Stepmania is, at its heart, a DDR compatible program that does a very good job of mimicking all of its features and adds a few new ones (that I pretty much couldn’t care less about).
What is kind of neat is that there is a gigantic selection of songs that fans have converted into the proper format. Unfortunately, about 90 percent of these songs are either poorly done (like scrolling so fast that you miss the arrow before you can see what it is), or have button combinations that would be impossible to pull off if you were using an actual foot-pad (like hitting three arrows at once). Of course people have also recreated the levels from the real DDR machines, which I suspect was the main impetus for the creation of this game, but I’m paranoid that way.