Garry's Mod
Publisher's Description
From Facepunch Studios:
Garry's Mod is a Sandbox Game based around the idea of building. Unlike most other games there aren't any objectives - you can't lose and you definitely can't win. Features:
Building.
Create constructions with moving parts. Create a car and drive it around. Create a rocket and fly it to the moon.
Single & Multiplayer.
Playing by yourself is fun. But playing with friends is even more fun! You can play Garry's Mod with your friends online, allowing you to cooperatively build together.
It doesn't have to be about building. It could be about finding terrorists. Or running a jail. Or playing football. There are lots of different gamemodes.
Download Addons.
Garry's Mod benefits from a rich productive community - so there's always new addons to try! Installing addons is achieved in a single click!
Ragdoll Posing.
Use the Physics Gun to move ragdolls and freeze their limbs. Place them in any position you want. Any Face Posing.
Edit the faces of ragdolls or NPCs. Make them happy, angry. Make their face stretch so much that every player on the server can see their bottom lip.