MUDs were your typical World of Warcraft type games where you ran around being a hero, solving quests and fighting evil orcs, except that you had no graphics to help you, everything you saw in game was a textual description of where you currently were and everything you did was typed in as a sentence to the game. You could have hundreds of people playing together, fighting and interacting, all without any form of picture ever being displayed.
MUDs were played using telnet, but to simplfy gaming using scripts, room maps and color coding MUD clients were programmed to improve gameplay. One of these clients was the SLClient, a Windows application programed with delphi.
SLCLient has since been open sourced, allowing others to use ideas and algorithms in other clients.
Project Page: Link