Ryzom Core is the open-source project related to Ryzom Game. Written in C++, Ryzom Core contains the whole code (client, server, tools) used to make the commercial MMORPG Ryzom. Ryzom Core is a toolkit for the development of massively multiplayer online universes. It provides the base technologies and a set of development methodologies for the development of both client and server code.
Ryzom Core is open source and released under the terms of the GNU Affero General Public License 3.0 (GNU/AGPLv3) for the source code and the Creative Commons Attributions-ShareAlike 3.0 (CC-BY-SA) for the art assets. Which means you can create your own game using Ryzom Core, for more information on doing so check out Creating Your Own Game Using Ryzom Core.