onModularloader is a very interesting on-line video synthesizer. It features full patching and real-time controls and very good documentation. This is an excellent platform for experimental video synthesis. The real time controls can be a little slow on older machines but experiment with different browsers.
The interface in the Modular Setup Mode looks like this:
onModularloader is located here: onmodularloader.
In the render mode with real time controls the interface looks like this: