Not the above, but I can chime in. Ragnarok Online private servers are (now) an entirely different beast than any of the official servers.

Automatic events, large custom maps, all sorts of fun player oriented stuff; custom classes, custom gear, new sprites for players and monsters, new colors all over the place, different balancing... All built on top of this ancient engine that's been ported and rebuilt a dozen or so times now.

Reading a bit of Ragnarok Online's private server history is very interesting.

The base experience yes, but people have been adding new functionality and mechanics to the world since the beginning of emulation.