This video (by Nocht) is definitely worth sharing for those interested in player-driven content in their MMOs. Peria Chronicles is still in its early stages, but what they've already got working is really impressive!
I don't quite understand the ability/skill system, but from the sound of it, you mix-and-match abilities based on the Kiranas (think Pokemon-like creatures) you obtain. I'm not much of a Pokemon fan, but to me it seems more like a thematic way to represent what is essentially a freeform skill-based character system (as opposed to class-based).
The world (or at least vast portions of it) seems equally malleable, with a system allowing players to create areas and structures. The tools appear to be fairly detailed, allowing you to even script events and actions - everything from custom traps to creating your own puzzles! It reminds me of what Landmark was attempting (though with even more ambition) before it was left for dead after the SOE buyout by Daybreak.
It'll be a while before there's an English version of the game (it's not even in Beta in its native Korean), but I'm intrigued by what we see here. This title is worth keeping an eye on to see how it develops.