Valve also no longer categorizes Garry's Mod as a modification, but rather as a full game, due to its ubiquity and popularity. Garry's Mod no longer requires one, although it is still possible to mount a game to be able to use its content.
Before this version, it was required to have at least one Source engine game. The current version of Garry's Mod is version 13, which still receives regular updates via Steam. Some even choose to remain in the sandbox mode to construct contraptions or scenery with the props and maps from most of Valve's games.
Many different game modes have emerged with many different objectives and styles. Being a sandbox type game there is no goal as such or a way to win, rather users can modify the game and play the mod however they wish. It allows the player to manipulate objects and experiment with the physics of the Source engine, often with interesting results due to the power of the engine.
Garry's Mod, or GMod for short, is a sandbox modification for Half-Life 2 but later became a stand-alone game.
