A turn-based grand strategy game in space: Defend Earth against an alien invasion from the edge of the Solar System. Negotiate with the various governments of Earth and secure their support - One way or the other. Establish your bases on other planets to take the fight to the enemy. Design and build powerful spaceships, then take them into battle.
You will design your own ships. Mastering this will make a great difference in the power of your fleet. There is no truly optimal build for all situations.