I just found out about this website by Phil Tulga. He's a music educator who created these tools for making music that cleverly integrates mathematical concepts like patterns and fractions with musical ideas like rhythm and pitch:
Unifix Drum Machine <a href="http://www.philtulga.com/unifix.html">http://www.philtulga.com/unifix.html</a> You get three drums, and click to make patterns. When all three drums sound together you get an unexpected rhythm. There are also built-in rhythms to listen to.