Garrysmod is a physics engine that enables the player free to do whatever their heart desires.It offers endless hours of gaming.You can make mods, maps, addons, playermodels, and much, much more.their are several fun gamemodes you can play in singleplayer or multiplayer(preferably).These gamemodes are Roleplay, where the player plays a role and must serve to his/her's best ability.Their is also sandbox. When you buy the game, you automaticaly get sandbox.It is basicaly just building and fooling around.The last gamemode im listing is Fretta and all the things under that.There are many things under fretta, but my favorite one is "Deathrun". There are a few selected players that become reapers, and are on the sidelines controling buttons and traps to try and kill all the players as they pass through.There are also many cool addons to have, and i strongly advise getting these if you get gmod. Wiremod andPhoenix Storms. I strongly reccomend this game to anyone Creative or just wants a LOL.