That Last Of Us | Almost Co-op
Many people have requested for The Last Of Us to be playable via Co-op (cooperation) mode. While Naughty Dog has not included the feature, the multiplayer part of the game was made with the intent of working cooperatively in a group of 4. All players will likely have a much better time when playing for the sake of the team rather that just for themselves.
So while The Last Of Us doesn't include a Co-op mode specifically, the core gameplay encourages players to work together, coordinate their attack, and offer support lest they be outplayed and beaten.