Websand is a simple JavaScript/WebGL implementation of a falling sand game which I made in a few hours. It is an extremely unpolished but reasonably functional prototype. I may clean this up one day.
To test, serve sand.html and load it in a browser. Click buttons to select elements and click and drag on the canvas to draw with the selected element.
You can also try this demo online at pineapplemachine.com.
Websand depends on twgl.
