Figure is a great new app that puts music creation into the hands of everyone, even non-musicians. It has a very unique interface that's easy to use and makes creating music a lot of fun. You slide your finger around a pad to play bass and lead, and tap columns to play the drums.
What makes Figure so great for non-musicians is that you will always be in the correct key and play to the beat. You get to be creative with the pitch and tones, but Figure will always make sure that your choices are "correct" musically.