CVG writes: "Stepping out of the singleplayer game of Garry's Mod and into the multiplayer realm is not for the faint of heart.
Why? Because the variety of gamemodes running on GMod servers is frankly daunting. This could easily have been a top 50, including Tic-Tac-Toe, Zombie Survival, Stalker, Dark RP, Violence Evolving... all spun together from shaky physics and the programming language Lua. We've reluctantly whittled it down to the choices below.
Happily, Garry's coding genius has made a game where all you need to play an entirely new gamemode is to join a server running one. GMod will update with the necessary files and you can play. So, enjoy the modes we've selected, but we also suggest you just randomly click around the server browser and see what comes up."