Pure Data looks interesting.

Pure Data is an open source programming environment for audio, video and graphical processing. I found the video above in the exhibition section of the Pure Data community portal, it was contributed by Pure Data user BrN. It would seem to demonstrate some of what the framework can do, though there’s not much else in the exhibition to compare it with.

Pure data was developed by Miller Puckette seems to be based on Max, though I don’t fully understand the relationship. Searching on the web, it’s difficult to discern a single ‘official’ page, but the community page, and Miller Puckette’s software page seem prominent.