America's Army: Special Forces is the US Army's own soldier training simulation online multi-player game.
You start the game offline as a new recruit going through the paces of basic training. Upon completion you choose your path. You can go online to start playing as a basic soldier. Or before you get "deployed", you can choose to go through some advanced training. The ultimate goal is to complete the Special Forces training to become a Green Beret. Going online begins the real part of the game as you join with other fellow soldiers and work on the missions which you choose.
As a military simulation, it's not a free-for-all first person shooter; you are bound by the Army's code of conduct in your behavior. Key to the game is not only your skills as an individual soldier but also how you perform as part of a team.