MapleStory (Korean: 메이플스토리) is a free-of-charge (with pay-to-play elements), 2D, side-scrolling massively multiplayer online role-playing game developed by the South Korean company Wizet. Although playing the game is free, character appearances and gameplay enhancements can be purchased from the "Cash Shop" using real money.
In the game, players travel the "Maple World", defeating monsters and developing their characters' skills and abilities as is typical in role-playing games. Players can interact with others in many ways, such as through chatting, trading, and playing minigames. Groups of players can band together in parties to hunt monsters and share the rewards. Players can also join a guild to interact more easily with each other.
Source: Wikipedia, "MapleStory," available under the CC-BY-SA License.