Just finished my first project using Pd-extended. It's a patch which allows you to select any combination of pitches, and it will randomly cycle through the pitches selected, at the set tempo.

I've made two versions, one which uses [makenote] to [noteout] which I've been using to play synthesizers in Ableton Live, and another which can work on its own using [osc~] to [dac~] (the latter isn't as refined, I just threw it together on a whim). I've included a feature which randomizes the velocity (volume in the second version) which gives a less stagnant sound.

To use it:
Select whatever pitches you feel like, and click Set (or press enter). If you want to select all octaves of a pitch, you can use the computer keyboard - a is C, w is C#, s is D, etc.
Make sure note length and velocity are not 0
Click On/Off or press the space bar to start and stop
You can also use the Manual button to cycle through pitches without a set tempo

Any comments and constructive criticisms are welcome!