What are some alternatives?
Sampulator - Make (and record) beats on your keyboard
BlokDust - Join blocks together to build sounds with this web-based music making app.
Silenz - Mix ambient noise in with the music you're listening to
Ramsophone - A generative art/music machine. (Be sure to refresh!)
Jammer - Turns songs into musical instruments anyone can play
Super Looper - Make music in your browser