Doom Builder is a free 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. Doom Builder is compatible with Windows 98, Windows 2000, and Windows XP operating systems. Version 1.68 was the last version of the original Doom Builder editor to be released. Doom Builder is no longer developed or supported and has since been deprecated by Doom Builder 2, which was released in May 2009.
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 "Build" editor. By aiming at the walls, ceilings, and floor, you indicate what you want 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 level designer 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.