Pong, with quantum mechanics.
This is a reimplementation of Pong: each player has a paddle, either left or right of the screen, which they can move up and down to control a ball which bounces around the 2D pitch. Each time the ball is behind a player's paddle, their opponent gets 1 point.
However the ball is a quantum particle: it is not represented by a solid volume but by a wave function, and nobody knows where it is precisely. Following the Copenhagen interpretation, as long as the game is in play, both players have simultaneously lost and won. At any moment of the play, either player can request a measurement that collapses the wavefunction to a point. If the ball is in one of the goal areas, the game is over, and the scores updated, otherwise the game just continues.
The (Re)Start button is used to kick-off the game, either at the very beginning, or after a goal is scored.
Player 1 (left) uses buttons 'A' (up) and 'Z' (down).
Player 2 (right) uses buttons 'K' (up) and 'M' (down).
The Space bar causes a measurement.
The Reset button resets scores to 0.