XMCP/1.1 server software for MOO - XMCP/1.1 is a simple protocol that allows structured messages to be sent from the server to the client. - http://www.awns.com/tkMOO-light/xmcp.html
XMCP/1.1 Applications - The main archive for XMCP applications and features an object browser, a mail reader, a chess game and a @who widget. - http://www.awns.com/tkMOO-light/applications.html
The MUD Client Protocol, Version 2.1 - Official documentation covers specifications, implementation, and information. - http://www.moo.mud.org/mcp/mcp2.html
MCP: Mud Client Protocol - Links to specifications and supported clients. - http://mcp.cubik.org/
MCP Implementation in zMUD - An overview of covered features. Includes links. - http://www.zuggsoft.com/zmud/mcp-dev.htm