About
Ryzom is a science-fantasy MMORPG for Windows, macOS, and Linux, developed by Nevrax and released commercially in 2004, before becoming free and open-source software in 2010. Ryzom Core is the open-source release of the C++ code behind the MMORPG Ryzom, including the full client, server, and development toolset rather than just a game client, and is usable as a base for building other massively multiplayer online worlds.
How it differs from the original
Unlike its original closed commercial release, the source code is licensed under the GNU AGPLv3 and the game's art assets under Creative Commons Attribution-ShareAlike, letting the whole toolkit be reused as a base for other games.
History
Ryzom launched as a commercial MMORPG in 2004 and was released as free and open-source software in 2010, with Ryzom Core continuing to develop that codebase.