Wind tunnel
Draw something and the air has to go around it. The simulation runs on your own graphics card, so it doubles as a hardware test.
Test my GPU turns the detail up one level at a time until your frame rate drops, then gives your graphics card a wind rating. It takes about 20 seconds.
It's a simplified fluid solver, closer to a toy than a real aerodynamics tool. Your GPU's name and your result stay in your browser.