MuSingWave

It does what it says. It creates lots of really interesting beats and lets you evolve them. Cool.
I found that when I unzipped the file, however, it didn't run. I had to change permissions on MuSingWave-OSX/MuSingWave.app/Contents/MacOS/MuSingWave to make it executable. Only then would it run. When it did run, the finder bar (MacOS X Panther) went transparent. I.e. I didn't have a File, Edit, etc, menu. I also had to force-quit it to make it go away. Bummer.
My big desire for something like this would be to save as MIDI instead of just as WAV, AU, or AIFF.