You can make it - Open Source MMORPG Platform
Open Source MMORPG Framework
An open source implementation of the Ultima Online Classic Client
Arianne is an engine to develop multiplayer online games like Stendhal
A multiplatform medieval 3D MMORPG
An open-source Phantasy Star Online server for *nix
Source of Mana is a unique 2D MMORPG
An unmodified version of the MMORPG Impressive Title by KovuLKD
Makes running a PSO server on Linux easier
Free MMORPG
Find the best oldschool server with the lowest ping [OSRS Live Ping]
An OpenGL client-server game
GameWhizzards is a user created, Open Source 3D MMORPG
Collection of Tools for Perfect World MMORPG
stro is an open-source cross-platform MMORPG server.
Dark Age of Camelot server emulator
World of Warcraft character converter, supporting multiple emulations
starrydb is game server engine
Python classes to work with Blizzards API
Immersive and expansive hardcore old-school 2D ORPG (MMORPG)
Massively multiplayer online game server and client framework