What are some alternatives?
Sampulator - Make (and record) beats on your keyboard
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).
Mubert - Electronic music generated in real-time just for you
Radium - Radium is a music editor with a new type of interface.
Ramsophone - A generative art/music machine. (Be sure to refresh!)
Lily - A drone with a camera that follows you. Throw it in the air.