The Discworld MUD was founded in 1991 and opened in 1992 to players by Pinkfish. It runs on a heavily modified LPMud Codebase, called the Discworld [MUDlib]] and is currently hosted at Ceres's House on a DSL Line, running on an Athlon 1.73G with 3 SCSI disks and 1.5G of RAM. The system runs Redhat Linux and Discworld uses the FluffOS driver (a fork of the LP MudOS driver)with the Discworld mudlib. Its player limit is set to 300 concurrent players (excluding creators).
It is a text-based game (No graphics whatsoever, beyond ASCII art) which requires a client to connect to it. There are many free MUD clients avaliable out there on the internet, but the official site also offers a JAVA Mud Client that can run through an internet browser.
Because the MUD has always been more focused on features than performance, this used to mean that LAG was legendary. However, with the advent of technology, the Disc is now relatively LAG free.
The MUD is basically an online Role-playing game, or possibly more similar to an Massively Multiplay Online Role-Playing Game, such as World of Warcraft or City of Heroes. The main difference is that it is entirely text-based; thus graphics are left up to your imagination, commands are typed rather than clicked all over the place, and players don't go 'OMG LVL 12 HEALER LFG!'
A partial reason for this is the levelling system in the MUD. As opposed to overall levels for your character (i.e. Level 1, Level 10, Level 60) the MUD takes note of your skills and your relevant level and bonus in them. The bonus is the number that determines how good you are at your the skill; this bonus is dependant on your stats and your skill level.