GURPS - Mars

From their website:

"The Red Planet. To the ancients, it was the God of War. To early astronomers, it seemed to be a world much like ours. To today's space explorers, it's the next step after the Moon . . . a harsh world that we might someday bring to life.

GURPS Mars describes Mars as it's been through the ages . . . as science now believes it really is . . . as it may be someday, mankind's first colony . . . and as the wild imaginations of science fiction writers have pictured it!

Five different settings provide a Mars for every campaign, from hard science to "Attack of the Bug-Eyed Monsters.""