Somewhere between Moore's Law and Soulja Boy, we saw this coming. As production equipment moved away from hardware interfaces to software applications, it was only a matter of time before it wound up in your pocket. And here we are. Apple's App Store is full of programs that allow you to create sounds, sequence and tweak those sounds, and record vocals over them to create a full song. We waded through most of them to come up with a solid list of seven music-creation apps that you should look to if you want to get your Just Blaze or Jim Jonsin on while on the subway. We're still waiting for the Soulja Boy x Fruity Loops iPhone app, but maybe that's just us.