Valve Hammer Editor, formerly known as Worldcraft and now commonly called Hammer, is Valve Software's map creation

Level design

Level design, environment design or game mapping is a discipline of game development involving creation of video game levels—locales, stages, or missions. This is commonly done using level editor, a game development software designed for building levels; however some games feature built-in...

 program for their game engine

Game engine

A game engine is a system designed for the creation and development of video games. There are many game engines that are designed to work on video game consoles and personal computers...

, Source

Source engine

Source is a 3D game engine developed by Valve Corporation. It debuted in June 2004 with Counter-Strike: Source and shortly thereafter Half-Life 2, and has been in active development ever since...

. Old versions of Worldcraft also supported Quake and Quake II

Quake II

Quake II, released on December 9, 1997, is a first-person shooter computer game developed by Id Software and distributed by Activision. It is not a sequel to Quake; it merely uses the name of the former game due to Id's difficulties in coming up with alternative names.The soundtrack for Quake II...

. Versions prior to 4 supported exclusively GoldSrc

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 ....

, 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

Source SDK

The Source SDK is a software development kit compiled by Valve Software that is used to create maps or mods for the Source engine, with the exception of Left 4 Dead, Left 4 Dead 2, Alien Swarm, and Portal 2...

, or downloaded the F2P

Free-to-play

Free-to-play refers to any video game that has the option of allowing its players to play without paying. The model was first popularly used in early massively multiplayer online games targeted towards casual gamers, before finding wider adoption among games released by major video game...

 first person shooter Team Fortress 2

Team Fortress 2

Team Fortress 2 is a free-to-play team-based first-person shooter multiplayer video game developed by Valve Corporation. A sequel to the original mod Team Fortress based on the Quake engine, it was first released as part of the video game compilation The Orange Box on October 10, 2007 for Windows...

.
Ben Morris created and released the original Worldcraft in September of 1996 as a tool for creating custom Quake maps.