You can download the latest version of Audiolet from GitHub.
Audiolet is awesome. It uses graph based routing and has lots of generators and effects and a sample-accurate scheduler and it supports sub-patches and pattern based composition and feedback routing and microtonal tunings and lots of other cool stuff.
Audiolet is simple. This is all you need to start making noise:
    var audiolet = new Audiolet();
    var sine = new Sine(audiolet, 440);
Audiolet is kinda cross-browser friendly. It works on Firefox >=4.0 and canary builds of Chrome with the Web Audio API enabled in about:flags.
Audiolet even has some some documentation! You can find a getting started guide and other tutorials on the wiki. There is also API documentation and examples to help you on your way.
Want to hear what Audiolet can do? Have a listen to examples of it in action by clicking here or here or here or here or here or here.
Audiolet was written by Joe Turner with the help of lots of amazing people.