A ton of stuff, primarily debug junk; but one can unlock all stages, give money to one's race, and change the image filters (black and white, oil painting). Since money is pretty much all that matters in the space and civ games, that's pretty much the "check's in the mail" cheat that people will use.
It does allow, however for someone to change any of the game variables. This might be interesting, but it does not list those variables for obvious reasons. But I'm betting we can do a lot with that if someone puts the time into discovering them.
