Music sequencing by drawing small towns: things by roads are noises; cars are your cursor. Currently in Flash; coming out for iOS soon. Worth checking out some of the best examples to see what's possible. It's a bit fiddly, but utterly delightful

Hard to explain, but a must-watch; lovely spatial music sequencer/toy. (And: I miss Offworld :( )

"Skittle-based beat sequencer, a tangible and edible music interface. This is a prototype developed over the course of two evenings, with a webcam and Processing." Fun!

"glitchDS is a FREE homebrew Cellular Automaton music sequencer for the Nintendo DS. It’s perfect for creating IDM and Glitch style loops." Should only work with R4, but seems to work with several carts.

It's a tracker. A tracker for Windows/OSX with VST instruments and effects support, a built-in sampler, and more. Certainly worth a play!