It’s been a while since posting…life eh! Anyway, I’ve been actively working on a synth toy/tool that works in the browser using only HTML5 and Javascript (and jQuery [yes this is also js :P], mainly to speed things up). It is here: http://ahsquared.com/synth/audiogen.html.
I have made no attempt yet at UI design or even any kind of prettiness, just getting the functionality squared away. This borrows heavily from a blog post by Steven Wittens for how to create and manipulate the audio samples.