AudioBox (www.get-me.to/nbm) is an audio scripting language that allows you to develop VST(effects)/VSTi(synths) plugins in a simple way. It is based on the traditional model of unit generators (oscillators, filters, envelopes, noise generators, etc..) which can be connected together to form anything you want, from a chorus effect to an additive synth.
It main feature is "compile" the user scripts in native VST/VSTi format.
It currently is in very beta stage, and have no documentation yet (sorry).

Inside the download package there is an example synth and a SDK (user can program new modules, but SDK is changing quickly)

Thanks.