Steer a fleet of ships to unravel Bell's spaceship paradox for yourself! See the Lorentz equations transform time and space before your own eyes! Experience time dilation and travel to a future world of pulsing clocks! Enable emissions to simulate fuel consumption! Aye, all this - and mayhaps more!
Worldlines is available for Windows, Mac, and Linux.
The worldlines handbook is available as pdf or html.
There be deeper waters still; our story may not end here...