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.
Sonic Pi does borrow (steal) a lot of ideas from Overtone. However, the goals are fundamentally different. Overtone aims to give you (the programmer) as much power as possible to create new instruments. Sonic Pi aims to be as simple as possible for everyone (including programmers) to use code to make music.
That said, we still aim to increase the power Sonic Pi offers. It's just that we'll not add any features that make it more complex than it already is without serious thought :-)
