Defence Alliance is a mod franchise for Unreal Tournament, Red Orchestra and recently Killing Floor.

Defence Alliance 2 features differant classes, such as the medic, rocketeer and mechanic.

The main game mode is played with two teams, one attacking and one defending. There are differant objectives to accomplish, such as destroyables and touchables.

New to Defence Alliance for KIlling Floor is co-op mode against specimens. The player has to survive the incoming waves of specimens. After a certain amount of killed specimens, the patriarch will spawn. When the patriarch has been killed, dead players can rejoin the match.

In both these game modes, players can setup their own defences, such as various turrets, like a cannon, minigun or rocket turrets. And the player can build ammoboxes, so the team can refill their ammo when they ran out.