A big part of calculus is examining a function's "rate of change", which itself is a function, called the derivative (of the original function).
In this game, get a feel for how the derivative (and its own derivative, and its own derivative) correspond to a function of position, all while driving your paying customers along a verrrrry long stretch of road.
WARNING: This game gets very fast, using LOTS of processing power for a web browser. Your browser may randomly crash while playing this (so play at your own risk).