Source (game engine)

The Source engine is a video game engine created by a company called Valve Corporation. The engine made its first appearance in 2004 with a game called , and was also included in Half-Life 2. Source has been worked on since that date, and is included in many of Valve's games.
Source is meant to power first person shooter video games, but has also been used to create other types of video games as well.
Features.
Source SDK.
Source SDK is a toolset used for Source engine. It has tools such as Hammer Editor, Model Viewer, and Face Poser.
Source Dedicated Server.
Source Dedicated Server is used to run multiplayer game sessions. It can work on Windows and Linux.
Valve Developer Community.
In 2005, Valve launched a website called Valve Developer Community. It is a wiki about how to use the Source engine.
Criticism.
Source SDK.
The Source SDK has been criticized for being out of date and hard to use.
Origins.
The Source engine originated from the GoldSrc, which was a changed version of John D. Carmack's Quake engine. Caramack said on his blog in 2004 that there's "still bits of Quake code in Half-Life 2".
Valve worker Erik Johnson explains the origins of the GoldSrc engine on the Valve Developer Community:
The Source engine then continued to replace the GoldSrc engine, until Source was mostly used at Valve.