Maplestory Adventures on Facebook
Mabinogi kinda has a feel of Maple, except when I played the EU server a long time ago I got hideously lost and had no idea on what my aims were or how to do things. (The very beginning of the game had some nice tutorials, but beyond the very start it just kicks you out the house and leaves you to it).
Dungeon Fighter might be somewhat similar, however I don't think it'd be your type of game, but what would I know as I've not played it myself.
Spoiler!