GoldSrc

GoldSrc, or Goldsource, is the retronym used internally by Valve Software to refer to the heavily modified Quake engine that powers their science fiction first-person shooter Half-Life.

GoldSrc is a modified version of the QuakeWorld engine codebase, which in turn is a development of the Quake engine codebase. Some minor fixes from the Quake II engine were incorporated as it was developed.

History of the name
While the engine has no official name, in the months before the release of Half-Life, many computing magazines described the engine as being based upon "Quake Unified Technology".

Erik Johnson explains the origin of the GoldSrc name in this quote from the Valve Developer Community:

"When we were getting very close to releasing Half-Life (less than a week or so), we found there were already some projects that we needed to start working on, but we couldn't risk checking in code to the shipping version of the game. At that point we forked off the code in VSS to be both $/Goldsrc and /$Src. Over the next few years, we used these terms internally as "Goldsource" and "Source". At least initially, the Goldsrc branch of code referred to the codebase that was currently released, and Src referred to the next set of more risky technology that we were working on. When it came down to show Half-Life 2 for the first time at E3, it was part of our internal communication to refer to the "Source" engine vs. the "Goldsource" engine, and the name stuck."

Evolution
The successor to the GoldSrc engine is the "Source" engine which powers Half-Life 2.

Licensed Games

 * Half-Life (Valve Software, 1998)
 * Half-Life: Opposing Force (Gearbox Software, 1999)
 * Counter-Strike (Valve Software, 2000)
 * Team Fortress Classic (Valve Software, 1999)
 * Gunman Chronicles (Rewolf Software, 2000)
 * Half-Life: Blue Shift (Gearbox Software, 2001)
 * James Bond 007: Nightfire (Gearbox Software, 2002)
 * Ricochet (Half-Life) (Valve Software, 2000)
 * Deathmatch Classic (Valve Software, 2002)
 * Day of Defeat (Valve Software, 2003)
 * Counter-Strike: Condition Zero (Valve Software, Ritual Entertainment, Gearbox Software], Turtle Rock Studios, 2004)