Garry's Mod (often abbreviated as GMod) is a sandbox physics game using a modified Source engine, created by Garry Newman. Garry's Mod has been available on Valve's content delivery service Steam since November 29, 2006. Purchase of 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 on YouTube, mainly from Team Fortress 2, Half-Life 2, Portal, Left 4 Dead and Left 4 Dead 2. Garry's Mod was originally a modification for Valve's Half-Life 2, but was later made into a standalone Steam game that was officially released on November 29, 2006 dubbed Garry's Mod 10. The current version, Garry's Mod 13, was released October 24, 2012.
In February 2014 it was revealed on Twitter by Newman that the game had "just broke" US$ 30 million. As of November 2013 the game has sold 3.5 million copies.