Garry's Mod, sandbox game, physics, Source engine, user-generated content, multiplayer, single-player, mods, Steam Workshop, ragdoll manipulation, posing, face posing, finger posing, prop placement, construction, Lua scripting, game modes, Trouble in Terrorist Town, Prop Hunt, DarkRP, Wiremod, creative freedom, interactive environments, community-driven, add-ons, custom maps, physics puzzles, machinima creation, dynamic lighting, 3D rendering, PC gaming, Valve Corporation, Half-Life 2 assets, user interface, in-game camera, screenshot capture, Steam integration, modding community, online servers, collaborative gameplay, Steam sales, gaming culture, sandbox experience, virtual experimentation, physics-based gameplay, content creation tools, Steam achievements, game development platform, player customization, in-game editor, physics gun, tool gun, spawn menu, game controller support, cross-platform play, virtual physics laboratory.