Bebot is still one of my favorite apps on the App Store, and mScribble, a recently revamped app from Appular and a developer named Panpipes Ho!, reminds me a lot of Bebot in its simplicity and versatility. That's pretty high praise indeed if you're as big a fan of Bebot as I am, but if you've never heard of Bebot, let me explain. mScribble is an app that generates a melody for you on the fly. The app plays a simple drum beat in the background with whatever rhythm you want -- there are nine to choose from in the app's menu). Drawing a scribble on the screen plays notes in a melody that's already lined up to the tune. It sounds complicated, but the app does all of the hard work -- just swiping across the screen gives you music, and with a little bit of practice, you can make some really interesting tunes by just playing around.
Unfortunately, it's not quite as friendly to professional musicians as Bebot. This is more of a music generator than an actual instrument, and there aren't as many options. Each tune can play four tones, but you're pretty hard-coded to the drums in the background. But that's a plus for less experienced players -- it means that anyone can sit there, swipe across the screen, and create an interesting melody. It's a lot of fun, and just the ten minutes of random joy I spent playing around with the app was more than worth the buck they're charging for it. I'd like to see the idea developed even further (and Bebot is an excellent model), but for just swiping up a tune, mScribble is a great experience.