Garry's Mod

Game description:

If you appreciate limitless freedom of action in a game, you've come to the right place! There is no single objective that you have to stick to in order to pass the game. You are just given virtual tools and the opportunity to create. Build the craziest constructions and design strange objects. Use a large arsenal of weapons and do it all for fun. Customize weather conditions and character behavior. All in all, it's a workshop where you can play with different items. You won't get so much pleasure from freedom in any other game!