This script helps you visualize time dilation and length contraction. It shows a side view of a stylized space ship traveling about the solar system, with stars in the background, set in the space ship's reference frame. As you set the speed of the ship, you can see how the time at your destination moves forward - so even though their clocks are running slow, a lot of time has elapsed on the planets before you get there.. As speed increases toward c, instead of going faster, the world is compressed.
If I wrote it today, I probably would have avoided perl-Tk, because it isn't installed on most computers.