I have been playing with Sony's Continuator, a MIDI Markov chain thingy. (more description of it here) There is a rather large quantity of little knobs and dials and settings to fiddle with. I haven't figured them all out yet. Sadly, I had the program in a state where it was producing gorgeous chords below what I was playing, and then it crashed, and I don't know how I got it in that state.