A simple WebGL raytracer. It's implemented as a a fragment shader, drawn on a quad that covers the viewport. Scene description and material data are fed to the shader in a truly barbaric fashion: as bytecode packed into a texture.
It's only been tested on a few platforms -- Firefox on Linux (Intel Graphics), Firefox on Windows (AMD Graphics), Chrome on Windows (AMD graphics). Since WebGL combines the variance of OpenGL with the variance of Web standards, it probably won't work on any other platforms it hasn't been specifically debugged on.