Impulse is a stark, frustrating, and very cool little game that's based on an amazingly simple framework that nonetheless creates surprisingly diverse gameplay.
It's a puzzler, in that each level you need to get from your starting location to a glowing green end; and the basic mechanics are those of Newtonian physics. You control a little blue ship, and your only controls are fore and aft thrusters, the direction of thrust being the line between your craft and the current mouse-pointer's location.
If that were all there were to it, it would be dull; but first of all, a number of simple variables are tweaked and vary with each level. You might have infinite fuel, or a limited supply; no time limit or a short one; have infinite hull integrity, meaning contacting the walls cause you no damage, or next to none, meaning any contact kills you. Gravity might be small, or harsh, requiring you to play more like Lunar Lander than Asteroids. Atmospheric drag might be nonexistent, or important.