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This lets you pilot a ship around a Schwarzschild black hole. (Click inside if it doesn't respond to you.) The arrow keys fire the rocket engines. Enter resets the ship. You get one point every time you catch the orbiting moon. Everything is from the point of view
of a fixed outside observer, but the "heartbeat" of the ship happens once per second according to the proper time on the ship.
Notice the outside observer never sees anything fall into the black hole; instead the ship just freezes at the event horizon, and its heartbeat slows to a stop as its proper time ticks arbitrarily slowly with respect to the outside time.