Rebound is a very simple one-player computer game, which I know is available for the Psion 5mx (for free, from CarrotSoft) and probably other platforms too. The playing field is a square grid, with blocks strewn in some of the squares (the grid itself is not displayed, just the blocks). The leftmost column of the playing field is alternating blocks and gaps, the column next to that has no blocks, and all the rest of the field has blocks at random.
A dot appears in a gap in the middle of the left of the screen, and moves steadily right (leaving a trail). It also falls down towards the bottom of the screen. When the 'thrust' key is pushed, the dot starts to accelerate upwards (at the same acceleration as the downward gravity). It continues to accelerate upwards until the key is released, then it is in free-fall again. If the dot bashes into the side of a block, it rebounds (a fully elastic collision - the sideways speed of the dot is constant). If the dot bashes into the top or bottom of a block, it rebounds but with a little less speed (an inelastic collision). The goal is to get the dot to the right side of the screen. If the dot leaves the screen on any of the other three sides, the game is lost. Points are given for the number of collisions the dot made on its way (the more collisions, the more points).
This is an interesting game in that there is only one control, and it's an on/off control at that. There are obstacles between you and your goal, some easy to get around, some tricky. If you miss a gap you're aiming for, you have to find another block or two to rebound off of to make another pass at it. And the trail the dot leaves can obscure the dot itself, if there's too much back-and-forth. There are two different 'dimensions' of difficulty; speed and block density. If the speed is increased, you need better reflexes. If the block density is increased, you need better planning. Improve one skill and the game can still try your weaker skill. The computer ensures that there is at least one path from the left side of the screen to the right, so if you lose, you've only got yourself to blame. This prevents a situation where you think you're doing really well, getting close to the goal, and then realise it's impossible - I hate it when that happens.