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: Sopwith is a side-scrolling shoot 'em up created by David L. Clark of BMB Compuscience in 1984. It was originally written to run on the IBM PC under MS-DOS. The game involves piloting a Sopwith biplane, attempting to bomb enemy buildings while avoiding fire from enemy planes and various other obstacles...
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: Enigma is a puzzle video game based on Oxyd, and is released under the GPL. Enigma continues to be very popular as an open source multi-platform derivative of Oxyd now that Oxyd is no longer maintained. The open source fangame Enigma has been praised in reviews. Enigma is a marble game. Wikipedia
Plot: Scorched 3D is a free and open source artillery game modeled after the MS-DOS game Scorched Earth. Scorched 3D offers a new game-play approach compared to the 2D original, such as: fully destructible ... Wikipedia
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...