I first played NexusTK in 1997, that's right 1997. It is one of the longest running MMORPGs out there, with a small community base and the most unique system in any online RPG.
The entire game, even the classes (outside the 4 base classes) are player run.
There are GMs, and developer run events, etc. But essentially the players run everything.
The game follows Korean History/Mythology very well and even spawned a live action series that is on Hulu.
For a game running this long, I'm surprised it isnt' already on this site :)
This game has been added to the system.