Adamant Entertainment's MARS. While it is not mean to be a translation of Edgar Rice Burroughs' Barsoom tales (although you can find that setting Savaged here), Gareth's setting still has a enough sword and planet action to spark the imagination. Of course, like many gamer's I've decided to tweek it slightly to match my own vision of the Red Planet.
In my MARS, most of the Gareth's setting is still intact: Mars is still a world of deserts, jungles, and ruined cities. Red men still fight fight the green savages of the wates as well as war with the White Apes. The Gray Men still plot and scheme in their dark, dank chasms and the Synthe-Men still tend their ancient machines. Callor, Baltan, Lonaria and the rest are still major centers of action and intrigue.
One of the notable differences between the Gareth's Mars and my Mars is the climate. Rather than being a cold and dry world, I've cranked the thermostat up to max and have the Red Planet bathed in nearly constant heat from an unforgiving, swollen, red sun.
Yes, you read that correctly. A red sun. Rather than setting it in the 19th Century or early 20th century, my Mars exists millions of years in our future. By this time our sun is entering the Red Giant stage of its life cycle and slowly swelling, engulfing the worlds of the inner solar system as it expands. Mercury is no more and Venus will be next in a few millions years. Earth is no longer habitable by anything we'd recognize as life, but the humans of the far future migrated to and terraformed Mars many eons earlier. For a time, Mars was a garden world and a haven for humanity until civilization fell into barbarism. Humanity's descendants, modified by the processes of natural selection and ancient genetic engineering, became the various intelligent races of Mars. (With the notable exception of the Grays, they aren't from around here.) If there are any "Earthmen" on Mars, they are part of the original Homo sapiens colonists who first came to Mars many millennia ago who have been somehow "preserved" (e.g. suspended animation tube), or they have been plucked from space and time by the Grays.
I'm also working on fleshing out the religions of Mars. Gareth made mention of one deity Faina the Provider, in the "Slavers of Mars" adventure. I plan on expanding the pantheon of deities a bit more, as well as work out the details of their particular rituals and practices.
Now that I've told you about my Mars, I want to hear about your Mars. Do you play the setting "straight up" or do you modify it like I did? If so how?