A new(and unofficial) sequel Dungeon Master Java is available. It's not
Open Source, but it might become that way. As you can probably guess, it is written in
Java.
It is a bit harder, has a plot, and comes with a really nifty level editor so you can make yet another Dungeon Master clone!
Get it at http://www.cs.pitt.edu/~alandale/dmjava/index.html