GLB is a free web based mmorpg, where basically you create your own players to play in human controlled teams in various leagues. It's pretty fun, especially if you enjoy American Football. You can also buy teams and control them, doing everything from stadium upgrades and scouting new players to setting advanced sub in/out tactics and pass/run ratios.
The 2nd season is nearing the end, and the 3rd season is about to start with some nifty new features. It's still pretty new but it's growing rapidly (I don't know the exact numbers, but I do know there's something like 100 000 human controlled players).
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goallineblitz.com]