Galcon Fusion is an excellent casual strategy game. I think it was originally released on the iPhone, with a version optimized for the iPad soon after. Then, versions for PCs, Macs and Linux computers were released. The game puts you in control of a planet in a solar system. Your goal is to conquer the whole system before your opponent does. It is a game of life or death. Each planet that you own generates ships. You start with a set number. The more planets you have conquered, the more ships you will have.
Conquering planets that aren't under anyone's control is easy and quick, but if you want to conquer your enemy's planets, you will have to send more ships than that planet holds. This sounds easy, but it can be tricky. You can send ships by clicking on the planet that you want to send the ships from and then the planet that you want to conquer. You can even select multiple planets at once to group all of their resources into a big armada of ships.
You can get the demo of this game from the developer's website or you can get the full version from the Mac App Store. This game is very popular there. I was expecting the lack of a touch interface to make this game harder to play, but I was wrong. The game plays just as smoothly on the Mac as it does on an iOS device.