Quick and dirty experimental toy.
For people asking schematic: I'm sorry but I don't have one. I've just built it like this looking at two other schematics:
1. Atari punk console: http://www.robthefiddler.com/electronics-audio-diy/circuit-experiments/atari-punk-console/
2. Baby sequencer: http://www.midiwall.com/gear/babyseq/
+ Extras: one more 555 as a clock for sequencer + noninverting opamp between sequencer output and atari punk console voltage control input.
So if you feeling adventurous and want to build one - go for it! It's not a rocket sience.