Doom Builder 2

Doom Builder 2 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. A script editor is also included for engines that support scripting. This product is developed 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 May 2009.

Doom Builder 2 is a complete rewrite of Doom Builder, with no code in common.

Forks
Three forks of Doom Builder 2 exist:
 * Doom Builder 64, created by Samuel Villarreal (Kaiser), supports mapping for the Doom64 EX engine but dropped compatibility with the other map formats.
 * GZDoom Builder, created by MaxED, is an extension of DB2 with support for many advanced ZDoom and GZDoom features, such as 3D floors, slopes, models, voxels, TEXTURES definitions, etc. It can still be used for non-ZDoom editing as well, with the appropriate configuration files, so it can be used as a complete replacement of the normal DB2.
 * 3DGE Builder, forked from GZDB, by Coraline, is a modified version hacked to only support 3DGE and Boom mapping. All other port capability, as well as all GZDoom-based functions and defs, have been stripped and are in the process of being fully replaced with languages and functions native to only 3DGE's advancements. The program is tailored to 3DGE, but can still be used as a replacement to DB2 for Vanilla and Boom mapping as those configs still exist. The program has the most recent version of glBSP for node building, as opposed to the other forks, built from 3DGE's Git repo.