Plot: Liquid War is an open source multi-player action game based on particle flow mechanic. Thomas Colcombet developed the core concept and the original shortest path algorithm, the software was programmed by Christian Mauduit. Liquid War 6 is a GNU package distributed as free software and part of the GNU...
Plot: Globulation 2 is a real-time strategy game, available in beta as of January 2009. The game updates on an irregular release cycle and is available in many Linux distribution's package repositories. The game minimizes gaming micromanagement by automatically assigning tasks to units. 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: kiki the nano bot is a puzzle game, a mixture of the games Sokoban and Kula World. It is available for Microsoft Windows, Linux, FreeBSD and Mac OS X. Wikipedia