I've been fiddling with Blender once in a while, which is free, but the learning curve is steep and I tend to give up after extruding a sphere or two. While I was looking up some related material I remembered Max/MSP which had a nifty kinda modular interface but costs oodles of money for honest law-abiding citizens such as myself. For some reason I looked that up on the Wikipedia and I find I have a low-budget modular video synthesizer right on my Mac. Quartz Composer is a fucking snap to use.
Share with me the fruits of my labours:
Autoplaying and looping YouTube is awfully fun.