I've been playing with Sonic Pi and loving it. It's by Sam Aaron, the same person who wrote Overtone (http://overtone.github.io/), a fantastic Clojure wrapper around SuperCollider (http://supercollider.sourceforge.net/) that adds many higher-level features. Right now, Sonic Pi looks to be a bit more limited than Overtone (more choices made for you, less access to low-level features) but I have a feeling that will change over time.