I found out that you can download Garry's Mod 10, 11 or 12 for

Garry's Mod Game - Keymailer

Steam Community :: Guide :: How to ACTUALLY play gmod

facepunch on X: Play Garry's Mod for free until the 18th December during our Publisher Event on Steam with a 33% discount on all our titles! / X

Steam Workshop::TOP 50 GMOD ADDONS #2

Garry's Mod - SteamGridDB

Increase Garry's Mod Performance (64-bit Guide)

How to let Gmod9 appear in your Steam library [Garry's Mod] [Tutorials]

i replaced the gmod banner image for my steam library with a realistic model of the average appearance of a psychopath. : r/gmod

Steam Workshop::[PM] Cameraman

Garry's Mod Steam Locomotive (Northern Class)