From Valve Developer Community
This game is included in the following packages:
Garry's Mod was born on the Something Awful forums. Although everyone had been enjoying JBMod, production of it had slowed down. Therefore Garry created Garry's Mod, a simple mod for Half-Life 2 in which the crossbow could rope things together and the pistol could shoot out manhacks.
Since then, Garry's Mod has advanced through 13 versions, each with more features than the last. The latest version has a massive host of features, such as easy ragdoll posing, keypads, doors, buttons, dynamite, welding, and just about everything needed to create contraptions as well as comics and machinima. It is now standalone and works on every Source game the user owns.
Garry's Mod itself has a large mod base. It supports Lua, which is used by fans to make new weapons, entities, and gamemodes. Gamemodes range in genre from roleplay, survival, sports and far beyond.
Garry's Mod is by far the most popular Source mod, and was the first mod ever distributed through Steam.
Garry's mod as a development tool
Garry's Mod is useful for Source developers, and can greatly fulfill certain tasks needed to make new mods. Tasks such as:
- A way to place and or move props in MAP_EDIT mode
- A user-friendly demonstration tool
- Chat with other modders and share ideas through text and usage of Gmod tools. Devs can use Gmod's tools to cooperatively share ideas about mod scenarios with players. Gmod can also be used to demonstrate a new map and discuss features without NPCs.
- Stress-test Source
- Use Gmod to test abusive usage of the Source engine, like spawning hordes of zombies, spamming explosive barrels and other intensive things. Will it crash? Will it freeze? Will the network buffer overflow?
- Quickly test game elements
- With the implementation of Lua scripting, you can create new game elements and weapons without using the Source SDK and make the process go a lot faster.
Garry's Mod is available on Steam. Garry and Valve split profits 50/50. There will likely be no retail version of Garry's Mod available.