Check out my latest game Air Traffic Control. Although the game is not completely finished because of some velocity issues, it can be played to the full. Also how to play is build in to game.
The problem with velocity is that it changes while playing a level and although it is set to the same speed it is different in the game levels. It has probably something to do with the amount of tasks the program has to perform.
I also need to tune the different game speeds.
If someone can help me resolve the velocity issue, help is much appreciated.