PianistEnvy developer Melonsoft has released
BubbleDrum 1.0, a drum machine application for Mac OS X and Mac OS 9 that has been developed for kids, hobbyists and musicians alike.
The BubbleDrum interface is called the Stage. You can create drums, arrange them and set properties including size, color, and which of sixty different drum instruments they emulate. Once your custom drum kit is set up the way you want it, you can either play by clicking the mouse or bind each drum to a key, then jam away. You can also save the kits you create.
BubbleDrum costs US$10 to register.