Edmap

EdMap is a DOS-based level editor written by Jeff Rabenhorst. The last update, version 1.40, was released on June 20, 1995. Features include:

Eric David Harris, one of the Columbine High School massacre perpetrators, thanked the creators in the credits of his "Deathmatching in bricks!" and "UAC Labs" WADs.
 * Support for the original Doom, Doom II: Hell on Earth, and Heretic.
 * Online help including a hyperlinked version of the Unofficial Doom Specs.
 * Shortcuts to allow fast mouse editing.
 * Good interface with support for texture/sprite WADs.
 * Very powerful, but uses only the 640 K conventional memory.
 * Easy to switch nodesbuilder by means of editing a batch file (default WARM).