The folks at the Capital SimCity forum have been working on a city builder. The latest updates show what looks like a lot editor for the game. It's all in Spanish, so a translator may be required. Have fun and flip through the 20+ pages and check out the pictures.
Monte Cristo attempted to make Cities XL into an MMO, didn't work out too well - the idea was good, the implementation was not. This is an article by PC Gamer that is a mildly interesting read: "Darkfall and a few other MMOs have proven that persistent city-building can work, with guilds proudly constructing, protecting and showing off their self-built cities."
During a late GDC 2011 panel about Raid on Bungeling Bay, the first game Will Wright developed in 1984, he said Sim City the original, began life as a tool for placing assets into games called "Wedit". Will Wright: “Wedit eventually evolved into Sim City,” he said. “I was scrolling around the world and having a lot of fun with it. I thought I’ll just buy one of these new computers, make a game on that, and level the playing field,”
And here we have the "SimCity" of our dreams, Baidu's hand-drawn 3d city maps: "Moving around the Chinese cities using Baidu's maps is a strange experience. There are no cars, no people; all you see are clean lines and beautiful skyscrapers. This is a utopian version of what the cityscape actually looks like." Stunning!