RainbruRPG is a 3D multiplayer Role Playing Game project based on Ogre3D and CEGUI. It is based on an Object Oriented design through C++ and Ruby modules and a community-oriented concept through a wiki.
Ryzom Core is a toolkit for the development of massively online universes. It was used to make the commercial MMORPG Ryzom. It provides the base technologies and a set of development methodologies for the development of both client and server code.
The Ileor MMORPG is a small MMORPG. The game is aimed at learning about the architecture of MMORPGs by building a simple one to play around with. With time, it might even be playable.
Cyphesis is a server for MMORPG games. It is the core engine of the WorldForge project and is currently focused on implementing fantasy games, providing rich scripting, full world persistence, and basic physics.