When I was 14 or so, a friend and I made up a game a game with magnets and steel ball bearings. The idea was to launch you ball bearing at the right speed and direction to navigate a series of magnetic barriers, and finally hit the target, which represented the other players "base". I don't think we ever had a name for it, but the idea in our heads was that this represented a battle in space, launching a missiles of into a complex gravity well to attack the enemy. Very low tech, but we had a great time with it.
Now you can get a very similar game right in your own browser, and it adds even more difficulty. Gravity Pods (not functional in my browser) has been out for several years, and now Gravity Pods 2 has recently been released.
This game lets you use gravity, repulsion, and reflection to guide a projectile from the launcher to the target. This forms a sort of puzzle where you use the laws of physics to guide your missile through a maze.
The game offers 50 levels, starting from the easy-introductory and working up to fiendishly-difficult. Some levels involve moving obstacles and wormholes that require precise timing as well as clever use of the available tools to solve.
The Gravity and Repulsion objects are particularly useful, but they have long range effects, so what at first seems to be the perfect placement can foul you up later. Some levels that at first appear very difficult turn out to have very limited ways they can be solved, and so are much easier than they appear. Of course, so that look easy, are not.
It's good fun, just don't start playing Gravity Pods 2 if you have something important to do, because you might be at it for a while. :-)
[Hat Tip to the Sciencepunk]