GoldSrc

GoldSrc (often stylized as GoldSource) is a proprietary game engine developed by Valve Corporation. It is a heavily modified version of the Quake engine, originally licensed from id Software. GoldSrc served as the foundation for numerous first-person shooter games, most notably Half-Life (1998) and its expansions, as well as early versions of Counter-Strike, Team Fortress Classic, and Day of Defeat.

The name "GoldSrc" came about internally at Valve as a way to distinguish the shipping version of the Half-Life engine from ongoing development and experimental builds. The "Gold" denoted the released, stable code, while "Src" represented the "source" material that would continue to be iterated upon.

While based on the Quake engine, GoldSrc incorporates significant changes and improvements, including skeletal animation, enhanced AI capabilities, and support for higher polygon counts and more complex environments. Valve continued to modify and improve the GoldSrc engine throughout its lifespan, adding features such as support for dynamic lighting, detailed models, and improved networking.

Despite being superseded by Valve's Source engine, GoldSrc remains historically significant due to its role in the success of Half-Life and its influence on the first-person shooter genre. Many games using the GoldSrc engine still maintain active online communities. The engine's relative simplicity compared to modern engines also makes it a popular choice for indie developers and modders.