The Free On-line Dictionary of Computing (30 December 2018):

LambdaMOO

    The most frequently used server software for
   running a MOO and also the nerve-center (of sorts) of the
   MOO community.

   (ftp://ftp.lambda.moo.mud.org/pub/MOO/).

   Telnet (telnet://lambda.moo.mud.org:8888).

   (1999-05-25)