Resource:GECK (program)

The official editor for Fallout 3 and Fallout: New Vegas, called the G.E.C.K. (Garden of Eden Creation Kit, named after the terraforming device of the same name from the series), that can be downloaded for free, allows PC users to create and add their own content to the game. The editor requires a pre-existing installation of the associated game to function, as it requires usage of several resources.

G.E.C.K. provides the community with tools that will allow players to expand the game. Users can create and edit any data for use with Fallout 3 or Fallout: New Vegas, from building landscapes, towns, and locations to writing dialogue, creating characters, weapons, creatures, and complex scripting.

The G.E.C.K. has an interface similar to The Elder Scrolls Construction Set, which is useful to those who are familiar with it. However, the functionality of the G.E.C.K. is far expanded over that of the Construction Set, much like the functionality of the game engine. Scripting options for the G.E.C.K. can be expanded using the Fallout 3 Script Extender or New Vegas Script Extender (or FOSE and NVSE, respectively) much like OBSE for TES IV: Oblivion and SKSE for TES V: Skyrim; however, these script extenders are not compatible with versions purchased via Direct2Drive, and having Games For Windows Live active will cause the game to crash as soon as you try to access Games For Windows Live.

Fallout 3 version
The Fallout 3 version was made available on December 11, 2008.

Patches
The G.E.C.K. was patched to version 1.5 in May 2009. The patch is available on the official site.

Fallout: New Vegas version
The Fallout: New Vegas version was made available on October 19, 2010, concurrent with the game's U.S. release.

Updates
You can now go to the official site and download it, it is now changed to version 1.4 and works. The G.E.C.K. is now available for download via Steam as of May 20th, 2013.