The Recoil Compensator is featured in Call of Duty: Ghosts, and it is only used in multiplayer. It is integral to the USR and L115 sniper rifles, and it reduces recoil; the reduction increases with each kill.
A ballistic computer is mounted on the scope, showing the recoil reduction. After the first kill, it displays a multiplier that increases with each kill, with the maximum being x4.
"Expels gases upward to aggressively fight muzzle climb."
The Compensator appears as a muzzle attachment in Call of Duty: Modern Warfare. It is available to all weapons that can accept attachments, with the exception of the Renetti handgun (which uses a different type of compensator) and the Crossbow.