Sampulator - Make (and record) beats on your keyboard
Ocean beta - Make music with friends in your browser
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
iO-808 - Rhythm composer modeled after Roland's TR-808 drum machine.
Ramsophone - A generative art/music machine. (Be sure to refresh!)
Cameo - Book personalized video shoutouts from your favorite people