Maplestory - MapleStory is among the most popular of MMO in the 2D area scrolling style offering a user count will into the lot of players.
Eden Eternal - Eden Eternal is a Fantastic Browser-based, Action-Adventure, RPG and MMO video game developed by X-Legend and published by Aeria Games.
LaTale - LaTale draws heavily from some other 2D side scrolling video games to provide a great fantasy MMORPG world.
4Story - 4Story is a Massively Multiplayer Online Role-playing, Fantasy-based and Combat video game by Zemi Interactive.
AdventureQuest Worlds - AdventureQuest Worlds (or AQWorlds) is an easy but very popular browser-based massively multi-player online Role-Playing game.
NosTale - NosTale (The Tale of Nomads of Silver Spirit) is a totally free MMORPG that includes simple (but beautiful) graphics and also lots of class options.