DoorMUD - The Land of the Forgotten
DoorMud Land of the Forgotten is very much like D&D. You have different classes and races and spells and Armor Class, and Health, Strength, Intelligence, and Dexterity. Weapons, Armor, and magical items that can be found.
Probably the best part is when you're playing and there's other players on! Yes, you can gang up on the monsters and defeat monsters that normally wouldn't be easy to take down!
Give it a try!