Overtone looks fantastic, and I've been meaning to really look into it for a while now. It seems to be an active project with a lot of momentum. I was writing something similar in Clojure, but more directly musically focused rather than on sound synths, before I found overtone. I tried installing it once a while ago, but had trouble getting SuperCollider to install and work with overtone.

Are there any overtone-related gatherings in the bay area?