I made a simple one nearly 20 years ago in Visual Basic 3 using a null modem cable and win 95 file sharing.
It's just a Multi User Database with some tweaks. Each record had a list of text "links" to other records. Planning the room layout on paper when you enter the data gives the dungeon impression. All the monsters were just computer operated users that traveled the same network of links. Then build on it like letting links link to scripts, adding the battle system. (I gave all items attack values, it was fun attacking my little brother with fuzzy dice and flowers.)
A few years ago I thought about porting the code to PHP. But I lost interest and the code.
I hope maybe this helps, if not, it was fun reminiscing.