Open Source MMORPG Framework
Arianne is an engine to develop multiplayer online games like Stendhal
Source of Mana is a unique 2D MMORPG
Collection of Tools for Perfect World MMORPG
Provides a full suite of clients and servers for virtual worlds.
This is the UI I use to play World of Warcraft
Python classes to work with Blizzards API
Runescape 2007 / oldschool client with many features.
The original Xivio.com World Server Core
PlaneShift Role Playing Game immersed into a 3D virtual fantasy world