Garrysmod

From BIGBIGHUGE WIKI

Garrysmod (or GMOD) is a game based on the source engine, it provides a sand box environment for experimental play with physics and props, it allows you to build contraptions like bath tub space ships, refrigerator trains and lounge chair roadsters, from props and character models from all valve source based games, provided you own the game that you wish to use the content from.

User and Community created content is built and encouraged including additional tools and game play written in the LUA scripting language.

Due to the nature of the game, killing is deemed inappropriate, even though weapons are prolific, it is proper decorum for players to inquire as to other players willingness to "Deathmatch" prior to doing so. Killing and destroying other peoples contraptions is known as Minge-ing and will get you banned on most servers.