AG36

The  is an underslung grenade launcher featured in Call of Duty: Modern Warfare 3 and was cut from Call of Duty 4: Modern Warfare.

Call of Duty 4: Modern Warfare
The AG36 was originally supposed to appear in Call of Duty 4: Modern Warfare, for the G36C, but was scrapped early in development. Its localization strings still exist in the game's code.

Call of Duty: Modern Warfare 3
The AG36 serves as the Grenade Launcher for the G36C, as first seen at Call of Duty XP. Not much else is known as of now.

Trivia

 * The AG36 looks similar to the M320 grenade launcher.