Normally when we talk about adding a ridiculous amount of players to a co-op game, it doesn't quite work out like we hoped.  The same can't be said for the military tactical game ArmA 2.   There's a mod in the works that is being dubbed as the "Headless AI Client" and it's allowing for some truly impressive battles to take place featuring dozens, even hundreds, of players with realistic and intelligent AI while still maintaining solid frame rates.