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.
Rogue Legacy - Rogue Legacy is a Fabulous, Action-Adventure, 2D, Platformer, Rouge-like, Side-Scroll, Exploration, and Single-player video game developed and published by Cellar Door Games.
Path of Exile - Path of Exile is a free to play online action roleplaying game that draws clear inspiration from Diablo but charts a path all its own.
Spelunky - Spelunky is an addictive, Rough-like, 2D, Platform, Side-Scroll and Single-player video game developed and published by MOssmouth.
LaTale - LaTale draws heavily from some other 2D side scrolling video games to provide a great fantasy MMORPG world.
Dead Cells - Castlevania-inspired, action platformer with roguelike elements.