Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Valve Hammer Editor, formerly known as Worldcraft and now commonly called Hammer, is Valve Software''s map creation program for their game engine, Source. Old versions of Worldcraft also supported Quake and Quake II. Versions prior to 4 supported exclusively GoldSrc, Source''s predecessor. The current version only supports Source. It is freely available to anyone who has purchased a Source based game as a part of the Source SDK.