MIT Game Lab researchers have been developing an open-source game called A Slower Speed of Light that simulates the relativistic effects of slowing down the speed of light. The first-person game has players navigate through a 3D space filled with orbs that reduce the speed of light in increments if you pick them up. It's a bit complicated, so I'll let the MIT researchers explain:
"Visual effects of special relativity gradually become apparent to the player, increasing the challenge of gameplay," said MIT Game Lab. "These effects, rendered in realtime to vertex accuracy, include the Doppler effect (red- and blue-shifting of visible light, and the shifting of infrared and ultraviolet light into the visible spectrum); the searchlight effect (increased brightness in the direction of travel); time dilation (differences in the perceived passage of time from the player and the outside world); Lorentz transformation (warping of space at near-light speeds); and the runtime effect (the ability to see objects as they were in the past, due to the travel time of light).
Here's a video of A Slower Speed of Light in action.
For more, check out the MIT Game Lab website.