What is MapleStory?
MapleStory is a free, two-dimensional, side-scrolling Massively Multiplayer Online Role-Playing Game developed by Wizet and distributed by various companies. The game takes place in the "Maple World," which players must defend against monsters. As in a typical online game, players can mold their characters to their liking by increasing their abilities. Interaction between users is encouraged in a variety of ways, including chatting, trading, and playing minigames.
Though the game is free to play, players may purchase various enhancements and upgrades in the Cash Shop using real money.
(Credit to MapleWIki)