Devobots -> Free
If it isn't free yet, it will be by 11:00 EST. There's some controversy regarding this app, its Kickstarter backers, etc. which I won't get into.
To the point: This falls into music/bizarre niche which I am so fond of. It's a synthesizer powered by an official(TM) Devo robot factory. Really...it's Devo. I can't explain it any better