Here is a list (although old) of MUDs servers and some descriptions. You may need to do some looking, but I am sure you can find source code out there.

http://www.lysator.liu.se/mud/faq/servers.html


Another option would be to research interactive fiction and then create a networked element to it. This is obviously more involved, but may be a fun and interesting project.



Hope that helps -


#dth-0