Doom Builder is a Doom level editor with full support for Doom, Doom II, Heretic, Hexen, Strife and all the popular source ports. Popular features include lots of customizability, prefabs, advanced drawing code, and a 3D Mode which lets you browse and edit your textures, and align them, in real-time. This product was created by Pascal "CodeImp" vd Heiden and is free software, licensed under the terms of the GNU General Public License. The project was first released in January 2003. It is no longer developed or supported and has been deprecated by Doom Builder 2.
In August 2003, Doom Builder introduced 3D Mode editing as a new concept in the Doom community. Map editing in 3D Mode is similar to the way you can edit in Duke Nukem 3D's editor "Build". By aiming at the walls, ceilings and floor you indicate what you would like to edit. With different keys and mousebuttons you can change the textures, texture offsets, sector brightness, ceiling and floor heights and much more.
John "Dr Sleep" Anderson, well known as game designer in different major gaming companies, wrote a detailed and comprehensive manual for Doom Builder in March 2004. The "Doom Builder Illustrated Guide" helps the beginner and experienced mapper to use Doom Builder and all of its features.
Doom Builder also comes with an advanced script editor for ACS and FraggleScript. This script editor can basically edit any kind of text-based lump when configured in the Game Configuration. The script editor has syntax highlighting, autocomplete and function definition tooltips.