Diku, Rom, Animud Area Editor
I wrote and worked on this mostly in the years 2002-2004. After that I made tweaks and used it to experiment with Java code from time to time.
This is a Swing implementation of an area editor for Roms, that could easily work for Diku or any other type of mud with some modifications.
Work did begin on forming a proper layer of abstraction. You should be able to separate some of the area behavior and provide an implementation for the services that depends on the type of mud area at runtime.
This code is provided as is, though emails and messages about it are welcome.
You can play Animud which is still running, but visiting https://animud.net or directly via telnet at animud.net:6667
Happy Mudding/Building! :-)