Via Grimwell I found the web-based game MyMiniCity. Well, it looks like a game, a bit like Sim City. Only there is no gameplay. The only thing you can do is to post links to your city in your blog, your forum sig, or wherever you hang out on the internet. At first you can only use a link that increases population, but then a link that increases industry becomes available, then transport, security, environment, and business. You are trying to get the biggest city possible, but of course your population needs all these things, and you need to get people to click on your link for your city to grow. And only one click per visitor per day counts. The only thing you get out of that is a ranking, you can try to have the biggest city of your country.
As Grimwell so correctly remarks, "Once you get past the goofy side of things though, there is a serious and almost smart business model here." It's the old dot.com "eyeballs are money" philosophy. Users are motivated to link to the site, creating lots of page hits, thus creating lots of views for the small banner ads. Note how I put lots of links to my city in this post to get you to click on them. I'm just fooling around here, but if I really wanted to grow my city, I would consider putting some link in the sidebar of the blog. MyMiniCity even offers XML and RSS feeds to support such things! Unfortunately besides growing your city and a small chat interface there is nothing you can actually do with your creation. It is social networking at it's most basic level, far, far away from Facebook or MySpace.