DIKUMUD  [codebase]
The root of the combat-MUD family. Levels, classes, equipment and area files —
and a licence that shaped a generation of derivatives.
https://dikumud.com/

Games we have identified as running this codebase
  35 listed, 0 archived
  /games?codebase=DikuMUD
  Measured in their handshakes: MCCP, MSSP, MXP, MSDP, GMCP

DikuMUD, written at Datalogisk Institut at the University of Copenhagen and
released in 1991, is the ancestor of most of what people mean when they say
"MUD" without qualification. Levels, character classes, hit points, mobs,
equipment slots, an area file format a builder writes offline — the whole
vocabulary comes from here, and games that have never seen Diku source still
inherit its shape.

Its licence is part of the story. Diku was free to use but forbade charging for
access and required the original credits to be displayed, and that clause is why
"the Diku credits" appear on the login screen of games several forks removed
from it.

The direct descendants — Merc, then ROM, CircleMUD, SMAUG, tbaMUD and dozens of
others — account for a large fraction of every MUD listing that has ever
existed.

WHAT IT LOOKS LIKE FROM OUTSIDE

The Diku family is the MSSP family. Where the MUSH side publishes a count
through a login-screen WHO and offers no MSSP at all, Diku-line servers
overwhelmingly answer telnet option 70 with a structured report, and that is
where their numbers here come from.

MCCP2 — stream compression — is also common in this family, and it is worth
knowing that a client which negotiates it but cannot inflate the stream receives
the entire connect screen as binary noise. That was a real defect in this
project's own telnet library and it is fixed; see MCCP
[/reference/protocols/mccp].

See also
  CircleMUD — /reference/codebases/circlemud
  ROM — /reference/codebases/rom
  SMAUG — /reference/codebases/smaug
  MUSH, MUD, MUCK, MOO — what the words mean — /reference/mush-mud-muck-moo