Steam link: https://store.steampowered.com/app/4000/
Short Description: Garry's Mod is a physics sandbox. There aren't any predefined aims or goals. We give you the tools and leave you to play.
Platforms: Windows Mac Linux
Developer: Facepunch Studios
Release: Nov 29, 2006 (17 years ago)
Genres: Casual, Indie, Simulation
Revenue Estimate: ~$170 million