This is the engine GMod 9 runs on. It is available for free in your Steam Library. Installation Guide
To download and play Garry's Mod 9 (GMod 9) , you can use the original free installer from legitimate community sources, but you will still need the installed to provide the necessary game engine files (Source SDK) . GMod 9 was the last free version before the game became a paid product. Prerequisites skachat garris mod 9 no steam
Find the line SteamAppId 220 and change it to SteamAppId 215 to ensure it targets the SDK base correctly. This is the engine GMod 9 runs on