The Map Editor was originally released on 22 November 2001 as a paid-for addon to Creatures 3 and Docking Station, available at the Creatures Mall. It can now be freely downloaded (direct link) at Gameware Development's website.
The Map Editor provides a graphical interface to manipulate rooms, metarooms and the doors between them. It stores the backgrounds in BLK files. The program will also generate CAOS and retrieve the map data from the game. A minor issue is that it displays low-quality versions of the backgrounds from generated bitmap files, instead of using the game backgrounds.
An official tutorial called Using the Map Editor is available.