A smouldering front creeping across a sheet: unburnt paper ahead, a narrow glowing char line where the reaction is, grey ash behind — with the glow a blackbody, so its colour and its brightness are the same number.
Drawn with: a WebGL2 shader.
Reacts to and looks like: gpu, webgl2 and audio-reactive.
Family: Visualiser.
Runs in your browser. The preview above is the same program the renderer uses.