What are some alternatives?
BlokDust - Join blocks together to build sounds with this web-based music making app.
Ramsophone - A generative art/music machine. (Be sure to refresh!)
Cycle - (taken from the man pages) DESCRIPTION
Google Music Lab - Interactive experiments that use the Web Audio API
Mubert - Electronic music generated in real-time just for you
Keezy Drummer - Make a beat in seconds