Tantalum, a beautiful, browser based ray-tracer

Tantalum is a 2D ray tracer that runs in the browser. Just click anywhere in the scene and watch those rays go a-scatterin' through the simulated optics.

You can reconfigure the contents of the scene, the light emission spectrum, and much else besides. The Secret Life of Photons, by creator Benedikt Bitterli, explains everything.

r/internetisbeautiful has some neat examples.