Galactic Civilizations I is FREE for a limited time! You can also get Gal Civ III, Offworld Trading Company, Planetary Annihilation: TITANS, Rebel Galaxy, and more in the Humble Intergalactic Bundle.
Or should we say, the Humble Intergalactic Planetary Planetary Intergalactic Bundle. (You didn't think we'd miss the chance to make this reference, did you?)
Humble Intergalactic Bundle