Garry's Mod Wikipedia :. Garry's Mod was originally a mod for Valve Corporation's Half-Life 2, but was later made into a standalone release in 2006 for Microsoft Windows, published by Valve Corporation. Initial release date: December 24, 2004. Publisher: Valve Corporation. Designer: Garry Newman. Developers: Facepunch Studios, Team Garry. Modes: Single-player video game, Multiplayer video game. Platforms: Microsoft Windows, Linux, Mac OS.