From Steam:
CITIES XL™ is the next-generation in city-building games, allowing gamers to develop cities on realistic 3D maps using an incredible collection of unique structures. Would-be Mayors are challenged to create the right combination of social services, leisure activities, special events and job opportunities within their cities in order to feed, employ and entertain their citizens.Realism will be pushed to the limit with cities that are bigger, more realistic and more sophisticated than ever before.
Up until March 8th 2010 the game was played online using a subscription based model but this was canceled due to lack of profits and a single player patch was pushed out to active players and is available for download. as a consolation they included a bus in the download.