By the guys who made Trickster Online:

Not exactly the kind of game I want to play but my brother has been playing this non stop for ages now. It's a side scrolling MMORPG like Maple Story, but it's just dungeons (no free roaming). And, you have to be a girl until you do some hard quest. But, if a few members join, I'll try it and we can do some dungeons together :3