Simulation

GamesRadar.com has a list of great commercial games that have been released for free.  Included are some of my favorites like Archlord, Battle Chess, Fallout, and many more. 

From the site:

We like free stuff. That’s why we posted links to download and play 365 free games so you could have a decent game to play for every day of the year, free of charge. Unfortunately, GamesRadar has yet to wrestle the most formidable type of free games into submission so that they can be preserved in their proper list form for eternity. We’re talking about the free games that were good enough to sell, important enough to review, and memorable enough to warrant a second play through years later.

http://www.gamesradar.com/f/30-commercial-games-released-for-free/a-20100202122153157099

Baseball Mogul 2007 lets you be the manager of a Pro, AAA, or High School team, even down to calling each pitch that is thrown. It was the best-selling baseball game in 2006, and it's now a free download. If you like accurate simulations, managing contracts, trading players, drafting, and like to play around with baseball statistics, this might be the game for you.

This version includes.

• Animated Play-By-Play
• Pitch-By-Pitch Mode
• Custom Pitcher Database
• Lefty-Righty Stats
• New Batter Rating System
• Improved Minor League Simulation Engine
• 2006 Opening Day Rosters
• Roster Tools
• Faster Simulation Speed

Baseball Mogul is the only game that includes every season from 1901 to the current season, complete with hand-edited rosters and ratings for thousands of major and minor league players.

Download Basebal Mogul 2007 for free at SportsMogul.com.

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.