This page contains most of the introductory information necessary for you to get a similar Mud working like "Land of Karchan".
The license I use for the mud is the GPL. As far as I know I am only using existing GPL or LGPL software to create my own software so this should be no problem.
Why do I give away the source code? Well, it's part of a new way of doing things. By keeping all source code private in the hands of companies you take away a piece of knowledge of which a lot of people can benefit. Try looking at it like instead of a company holding back the formula to the solution to a disease, having the company give out the formula for public use, thereby helping people all over the world. A lot of my source code is based upon other people's source code, who basically did the same thing as me, thereby creating a base on which I could build my mud.
The java documentation ("javadoc") of the backend is available here.
The typescript documentation ("typedoc") of the frontend is available here.
I'm giving you the source code of my mud in order for you to make something original with it. There is a clear distantiation between my mud (Maarten's MUD) and the Land of Karchan. While Maarten's Mud does fall under the GPL, Land of Karchan does no such thing and is copyrighted by me and others.
Have fun experimenting, and do send me an email if something is not clear.