A friendly chat image - Garry's Mod ScreenShots & Movies

Garry's Mod (officially abbreviated to GMod) is a sandbox physics game using the Source engine. Garry's Mod has been available on Steam's content delivery service since November 29, 2006. Despite being a standalone game, Garry's Mod requires the user to own at least one game on Steam based on the Source engine, such as Half-Life 2, Counter-Strike: Source, Portal, or Team Fortress 2. It is also commonly used for the creation and publishing of videos/screenshots, mainly from Team Fortress 2, Half-Life 2, Portal and Left 4 Dead.