Played here every day until university whittled away all my free time. Been playing MUDs since 1992 and this is the best codebase/setup I've seen yet:
Myrradel is a heavily modified UltraEnvy all-playerkiller MUD. With a subclassing system, players can choose to become more specialized in their class after level 30. Spellcaster players, after a certain level, can learn spells from spellbooks to even further individualize their character.
Myrradel is a power MUD in which players strive to beat each other through the enhancement of their skills and the development of their characters. Players continue to enhance their statistics, far after reaching the maximum level of 60, in an attempt to beat the unthinkable mobs as well as to become king of their class.
Realms of Myrradel
or telnet to myrradel.ocliw.com 4000 to jump right in.