Xavier Shay's SocialBeat app allows you to livecode OpenGL in Ruby, and control that OpenGL with MIDI at the same time. This screencast illustrates some rough, proof-of-concept example material.
This is one of the roughest, messiest screencasts I've ever done. You'll think I was drunk. But it's worth watching anyway. This is a very innovative app. The flattering part: Xavier told me he got the idea from my RubyFringe presentation on Archaeopteryx.