Garry's mod

Garry's Mod or GMod is a modification for the Source engine. It is a physics sandbox game that allows the player to manipulate objects and experiment with physics.[1]

Garry's Mod requires the user to own one Source engine based game (games including Source SDK), such as Half-Life 2, Half-Life 2: Deathmatch, or Team Fortress 2, and that the Source game has been used at least once. This ensures that the necessary program files are provided to Garry's Mod. The game can be bought in a pack bundled with other Source games or purchased over Steam.

Offical site :

Kod:

www.garrysmod.com