Garry's Mod (officially abbreviated to GMod) is a sandbox physics game that allows the player to manipulate objects and experiment with physics using the Source engine. Garry's Mod has been available on Steam's content delivery service since November 29, 2006. rnDespite 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 2, or Team Fortress 2. It is also commonly used for the creation and publishing of videos on YouTube, mainly from Team Fortress 2, Half-Life 2, Portal and Left 4 Dead.