Beads.js currently only uses the Mozilla Audio Data API, available in Firefox 4, for generating sound. Later on it may support other browsers with a Flash or Java audio engine.
The current development code of Beads.js is available in a Mercurial repository; go to http://hg.chrismorgan.info/beads.js/ for that.
The code can also be tested directly online here.
To view (or rather, to listen to) examples of Beads.js, you will need a recent build of Firefox 4 (Beta 5 or later or a nightly build after the 26th of August). Having Firebug is also recommended.
Beads.js is also not stable yet; it is possible that some examples may break from time to time. Also it is not yet rock-solid. If the system has much other activity running on it audio output may be choppy for more complex examples.
Examples are available here.