"Action is a multiplayer-only modification, or mod, for the retail first-person shooters Quake 2 and Half-Life. The name Action comes from the mod's theme of high-adrenaline motion pictures, especially those featuring
lots and lots of gunplay. From the realistic settings and weapons, to the intricate attention applied to the
almighty spin kick, an atmosphere smack-dab in the middle of an action-filled movie awaits the player."
--The A-Team, creators of AQ2 and AHL.
There are two brands of Action at this particular moment; the first was and still is Action Quake 2, and the second is Action Half-Life. The next predicted release is Action Unreal Tournament.