You can make it - Open Source MMORPG Platform
Open Source MMORPG Framework
An open source implementation of the Ultima Online Classic Client
LSJ-Server-Terra (Java Multipurpose Sever connected with MariaDB)
A multiplatform medieval 3D MMORPG
A suite of tools to make running a AzerothCore server on Linux easier
Source of Mana is a unique 2D MMORPG
An open-source Phantasy Star Online server for *nix
Arianne is an engine to develop multiplayer online games like Stendhal
GameServer is a sophisticated, game server designed for online games
An unmodified version of the MMORPG Impressive Title by KovuLKD
Makes running a PSO server on Linux easier
Free MMORPG
An OpenGL client-server game
Collection of Tools for Perfect World MMORPG
starrydb is game server engine
Python classes to work with Blizzards API
Massively multiplayer online game server and client framework
Blender port of Ryzom art data
Open source server for Other Life/Eternal Lands client