Open Source MMORPG Framework
Arianne is an engine to develop multiplayer online games like Stendhal
An open-source Phantasy Star Online server for *nix
Free MMORPG
Collection of Tools for Perfect World MMORPG
Python classes to work with Blizzards API
Blender port of Ryzom art data
The original Xivio.com World Server Core
Modular Minecraft server plugin - commands, events, ...
Create your own online real-time browser-based MMO in your website
Frontend for Minecraft Server