Cities XL is a lot like SimCity, but with a persistent online environment for players to take their God-complexes online. Beta sign-up starts today and we've got your bonus code right here.
Go to the sign up site and type in: KOTCXLBR. It won't guarantee you a beta slot, but it will increase your chances of getting in.
The online mode in Cities XL lets users pick a planet with preset environmental conditions (like water-to-land ratio, explosive volcanoes, high seismic activity, etc.) and build a city from the ground up. Players can interact with each other by sending their "Mayor" avatar to visit other user-made cities, or by setting up trade systems between cities.
For more details as well as info on the singleplayer mode, check out this preview.