GSN Composer

The GSN Composer is a free online node-based visual programming environment for rapid prototyping and interactive demonstrations. Typical areas of usage are education, research, entertainment, special effects, or arts. 

+ Node-based interactive visual programming
+ Extendable with custom JavaScript plugin nodes 
+ WebGL support
+ Integrated GLSL Shader Editor
+ HDR image pipeline
+ Modular synthesizer with MIDI support