I’m not sure about this, I was in two minds about posting it as it looks a bit toy like (not that I have anything against toys), but on balance I think it may appeal to people, and it is free.
Here’s the app’s description:
Indiloop is the easiest way to make your own remixes and mashups. Just find your favourite artists and start combining stems into the mixer. Look you just made a song! Feel like a rockstar yet?
Indiloop on the app store, free …