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.
Realm of the Mad God - Realm of the Mad God is a best online hack and slash video game that includes pixel style graphics.
LaTale - LaTale draws heavily from some other 2D side scrolling video games to provide a great fantasy MMORPG world.
Stendhal - Stendhal is an Action-Adventure, Massively Multiplayer Online, Role-playing, Browser-based and Fantasy-themed video game that provides you with old school visuals style.
AdventureQuest Worlds - AdventureQuest Worlds (or AQWorlds) is an easy but very popular browser-based massively multi-player online Role-Playing game.
Luvinia - In Luvinia World players will explore vibrant and huge maps in a 3D fantasy setting.