Plot: PlaneShift is a cross-platform 3D Online Multiplayer Role Playing Game in a fantasy setting. The framework is open source with the server and client released under the GNU General Public License v2, while the artistic content is covered under a proprietary license. All content, however, is available...
Plot: Eternal Lands is a free, multiplayer, online role-playing game created by Radu Privantu in 2002. A pre-alpha version was made public on February 13, 2003. The game client is written in C using OpenGL and SDL. Wikipedia
Plot: The WorldForge project is producing an open source framework for massively multiplayer online role-playing games. The intent lies in creating a widely used development framework and set of libraries by motivating interested developers to improve on the original source code. Wikipedia
Plot: Egoboo is a 3D open source dungeon crawling action role-playing game with support for Windows XP, Windows Vista, Linux, Mac OS X, and some earlier versions of Windows. Wikipedia
Plot: Lincity is a free and open-source software construction and management simulation game, which puts the player in control of managing a city's socio-economy, similar in concept to SimCity. The player can develop a city by buying appropriate buildings, services and infrastructure. Wikipedia