GMod is a Sandbox Modification. Using GMod you can pose ragdolls. This means can position people from HL2/CS/DoD and change their faces. A big comic book creating community has popped up around this feature. Using GMod you can build. Take props from HL2/CS/DoD and weld them together to make walls. Axis a wheel to it to create a working car. Rope some cans to the back. A big contraption creating community has popped up around GMod - creating such things as Rube Goldberg devices, catapults, cannons, bridges etc.. Using GMod you can make your own weapons. That's right, make your own weapons. Using Lua you can create a custom weapon to do just about anything. If you're new you can change simple things like rate of fire, models, sounds. If you're awesome the world is your oyster, mass changing guns, melon cannons, jetpacks. GMod gives you the freedom to do any of these things in single player or online with your friends.
A simple Out-Of-Game Tool that let's you set options for multiple Source Games at once, and even let's you set options that are not normally available. Great for many uses. Note: I did not make this tool, and I am uncertain wether or not that it works on Linux or Mac, as I use Windows. The tool was originally uploaded on Planet Half-Life, and all credit goes to Kapitein Iglo, not me.
I did not make the tool, all credit goes to Kapitein Iglo, a Planet Half-Life User.
Now you can set options for multiple Source Games at once, great if you got new mods and games and don't want to launch them individually just to set options. Works with Mods too!