A game by Brian Hollenbeck, Time Traitor was written for the Game Chef 2006.
Imagine that time is a towering spiral of water, arcing through a vast void, and disappearing into infinity at either end. You can move freely along its graceful curve, dipping in and out of it at will, making no wave or ripple. You can watch dinosaurs grazing in Pangaea; the Battle of Hastings; the day when two thieves and another man were crucified on Golgotha. All that ever was is yours to observe, and record.
Touch the column, though ? interact with it, change it, and ripples begin to flow up the column, towards the present. They begin slowly, gaining momentum and power, until some years or centuries or eons in the future, the column shatters into a fine spray of droplets, vanishing into the void.
Now you know the power of time travel, and you understand the First Law:
The Past Cannot Be Undone.