A world in outline, and a cursor. Click and tiny humans arrive on the ground you clicked, each with their own shadow and their own short thing to say. Click more and there are more of them. There is a button that produces a great many at once and a button that removes all of them.
Nothing is being scored and nothing is at risk. It is a sandbox in the original sense of the word, closer to shaking an ant farm than to playing a game, and the pleasure is in the density: a dozen humans is a scene, two hundred is a civilisation, and the difference between them costs one click. Fifteen minutes, or considerably longer if you have somebody to show it to.