MUCK  [codebase]
A TinyMUD descendant with its own Forth-like in-game language, and a social
culture distinct from the MUSH side.
https://www.fuzzball.org/

Games we have identified as running this codebase
  24 listed, 0 archived
  /games?codebase=MUCK
  Measured in their handshakes: MSSP, MCCP

MUCK — in practice almost always Fuzzball MUCK — is a sibling of the MUSH line
rather than a descendant of it: both come from TinyMUD, and both put a
programming language inside the game.

The language is the visible difference. MUF (Multi-User Forth) is stack-based
and reads nothing like MUSH softcode; a builder fluent in one is a beginner in
the other. Above it sits MPI, a smaller inline expression language used for the
things softcode would do on a MUSH.

Culturally, MUCK is the home of a large part of the hobby's social and fandom
worlds. Those games tend to be built around presence and conversation rather
than around scenes with a start and an end, which is a real difference from the
roleplay MUSH tradition and not a matter of theme.

WHAT IT LOOKS LIKE FROM OUTSIDE

No MSSP. A pre-login WHO that answers with a count. No telnet options negotiated
on the game we measured — and one detail from the survey worth keeping: its WHO
reply ended in a trailing space with no newline, which is the kind of thing that
makes a naive parser report nothing at all.

See also
  MUSH, MUD, MUCK, MOO — what the words mean — /reference/mush-mud-muck-moo
  TinyMUSH — /reference/codebases/tinymush
  MOO — /reference/codebases/moo