ephenation-server
Ephenation is a MMORPG client-server game. The purpose of the game is to support adventures in an unlimited world and for players to create their your own adventures. The server is designed to handle large amount (~10000) of players.
The server is designed to run on a Linux platform, and the client is designed to run on both Windows or Linux (based on OpenGL 3.3).
See Ephenation wiki for more documentation. There is a page about the game progress at Google+ and a blog about some of the OpenGL experiences Ephenation OpenGL.