I'm not sure I've sound that yet, but I did find Pure Data (Pd). And I mention it here partly because of the music tech aspect, but partly because their description of it reminded me of something Josh has talked about:
Pure Data is an open source visual programming environment that ... enables musicians, visual artists, performers, researchers, and developers to create software graphically without writing lines of code. ... It is suitable for learning basic multimedia processing and visual programming methods as well as for realizing complex systems for large-scale projects.
Among other things, it looks like Pd was used to do generative music in Spore and Darkspore. But it's the idea that this is a general visual programming system that got my attention.
Has anyone here poked around with this yet?