Indeed, Magic Piano, another popular iOS Smule app that has now made its way to Android, lays out a series of dots which you have to tap in tune to your favorite song (assuming it's in Smule's inventory, of course).
So, Songify - have you heard about it? It's pretty popular on iOS, something 9 million people love it (or so I've heard). Basically it's autotune, but more fun. What's more fun than autotune, you ask? Autotune plus music, that's what.
It's pretty simple: you speak into the app, and it autotunes your voice, puts it to music, and randomly loops it. The end result is actually quite a bit more humorous than I expected.