There's a commercial program called 'PerlMUD', by Tom Boutell, of gd fame. I remember first seeing it, and that was 8 or 9 years ago, so I've no idea what state it is.

I've contemplated the question of how to write a MUD in Perl many times - although I've never even started writing one. Writing a MUD in Perl could mean one, or both of two things: writing the framework in Perl (that is, the thing that keeps the MUD running, similar to for instance 'MudOS', 'DGD' or 'Amylaar') and the language of the MUD itself (instead of for instance LPC or Pike).

I'd first decide what kind of MUD I'd write (and I don't mean the theme, but essentials like can 'anyone' contribute code (for instance in traditional LP muds, anyone reaching level 20 becomes a wizard and can start writing code) or can only 'trusted' people add code? Should the MUD be able to expand/upgrade on the fly (like LP) or does it require a reboot/restart (like Diku)? Only after deciding such questions, I'd go shopping for software.