Nation States -- A free simulation game

NationStates.net is a online game where you can create and run your own nation. From the website:

NationStates is a free nation simulation game. Build a nation and run it according to your own warped political ideals. Create a Utopian paradise for society's less fortunate or a totalitarian corporate police state. Care for your people or deliberately oppress them. Join the United Nations or remain a rogue state. It's really up to you.

They seem to have a really great community going, and the pictures of in-game content on the forum look great. It looks like they are doing a pretty good job of letting you create and run a complete nation. You can even create your own adventures.