The overtone project was started around 2009 by Jeff Rose, joined by Sam Aaron who worked on it full time for a year as part of a principled research project at the University of Cambridge. Sam has now formed a band Meta-eX with Jonathan Graham, mixing live coding with live controllers like the monome. Meta-eX are already playing across Europe, and there are rumours of them preparing an algorave set to hit London in the next month or so.
Overtone has tight integration with its Sister project Quil, a Clojure front-end to the Processing API — good for those audio/visual live coding sessions. Great stuff and definitely worth a look for the incredible README.md file alone.
The Overtone community is growing fast, and now Toxi, the generative/interactive art hero behind toxiclibs, has got involved too, running a workshop on Overtone and Quil at the Resonate festival. If you want to check out Overtone his workshop materials might be worth a look. Note though that the overtone documentation is good, and the excellent emacs live environment is itself designed to support an exploratory style of learning.
If you are intrigued though, your first port of call should probably be this 4 minute whirlwind of an intro video: