Doom Construction Kit

Doom Construction Kit is a sector-based DOS level editor created by Ben Morris. It is similar to the Doom Editing Utilities tool in many respects; for example, DCK is mode-based.

Versions of DCK prior to 2.2f were freeware; those released afterwards required payment. However, older versions can still be downloaded and have the same features as later versions.

(The Waite Group published an unrelated book also called "The DOOM Construction Kit".)