The Rubik's Cube has been the world's best-selling puzzle since Ernő Rubik invented it in 1974, and it's a natural fit for a browser: a 3D cube you can rotate freely, scramble with a click, and solve with the mouse. A timer records how long you take.
There are 43 quintillion possible arrangements and every one of them can be solved in twenty moves or fewer — the famous 'God's number'. Learning to do it yourself takes an afternoon with a layer-by-layer method and a lifetime to do quickly.
The beginner's method solves it in layers: the white cross, then the white corners, then the middle layer, then the yellow cross, then orienting and permuting the last layer. It needs about five algorithms in total.
Twenty. It was proven in 2010 that any scrambled Rubik's Cube can be solved in twenty moves or fewer, no matter how it's arranged.
Yes — drag a face to turn it. It runs in any browser with nothing to install.