As promised, the CitiesXL demo has gone live today. The demo will be available throughout the month of September and will allow players to try out three of the 25 solo mode (50 for Planet Offer) maps, and build cities with a population cap of 22,000. The full game will allow for megalopolises with millions of citizens, among other things.
The game client is available at the following mirrors:
More information on CitiesXL can be found at the game's official website, here.