"Project Reality: Battlefield 2 is a free-to-download single and multiplayer game modification for the Battlefield 2 (BF2) retail Microsoft Windows PC game. Project Reality installs alongside your existing Battlefield 2 game installation, allowing both the original game and Project Reality to be played separately without conflict." - http://www.realitymod.com/
It is basically like Arma but free. It is very realistic and strategic. If you run around this game like a headless chicken , you will die.... a lot. It does take a while to learn all the controls but it is a very fun game. Note: You need a mic to play this game.
Here is the website: http://www.realitymod.com/
If anyone else is interested we could then squad up some time and have some fun.