MSDP  [protocol]
The Mud Server Data Protocol — the same job as GMCP, done with a compact binary
encoding and a discovery mechanism GMCP lacks.
https://www.mudhalla.net/tintin/protocols/msdp/

Measured adoption
  96 of 886 listed games were observed offering it (10.8%)
  /games?protocol=MSDP

  The games not counted here are not games without the protocol. A game is
  counted when we observed its server offering the option in a handshake; the
  rest are servers that did not offer it to us and servers whose handshake we
  have not read, and we cannot tell you which.

  By codebase, of the games we identified
    CoffeeMUD            16 of 32 offered it
    Evennia              11 of 11 offered it
    CircleMUD            9 of 47 offered it
    ROM                  6 of 55 offered it
    SMAUG                5 of 20 offered it
    tbaMUD               4 of 5 offered it
    DikuMUD              3 of 35 offered it
    AresMUSH             0 of 18 offered it
    CobraMUSH            0 of 2 offered it
    FluffOS              0 of 28 offered it
    MUCK                 0 of 24 offered it
    PennMUSH             0 of 34 offered it
    RhostMUSH            0 of 40 offered it
    TinyMUSH             0 of 9 offered it

MSDP is telnet option 69, and it solves the same problem as GMCP
[/reference/protocols/gmcp]: sending structured data alongside the text so a
client does not have to scrape prose for numbers.

The differences are two. MSDP's encoding is binary and compact — variables and
values are marked with single control bytes rather than wrapped in JSON — and
MSDP defines a discovery conversation: a client can ask LIST for COMMANDS,
REPORTABLE_VARIABLES and so on, and be told what a given game supports. GMCP has
no equivalent, which is why a GMCP client generally has to be configured per
game.

In practice GMCP won on adoption and MSDP persists in the servers and clients
that implemented it, often alongside GMCP.

WHAT WE MEASURE

A game counts here when its server offered MSDP in a handshake we observed. As
with every figure in this section, that is a positive observation and the
remainder is not its opposite — a game not counted may not implement MSDP, or
may simply not have had its handshake read by us yet.

See also
  GMCP — /reference/protocols/gmcp
  TinTin++ — /reference/clients/tintin
  Blightmud — /reference/clients/blightmud