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: Glest is a free and open-source real-time strategy computer game from 2004. Glest is set in a medieval fantasy world with two factions, and was compared with Warcraft III and the Empire Earth series. Wikipedia
Plot: Danger from the Deep, often abbreviated as DftD, is an open-source World War II German U-boat simulation for PC, striving for technical and historical accuracy. Wikipedia
Plot: Vega Strike is a first-person space trading and combat simulator, developed for Microsoft Windows, Linux, FreeBSD and OS X systems. Many of the core game mechanics of Vega Strike are indirectly inspired by Elite. Other games, such as Wing Commander: Privateer, influenced the original developer. Wikipedia...
Plot: Armagetron Advanced is a multiplayer snake game in 3D based on the light cycle sequence from the film Tron. It is available for Linux, macOS, Microsoft Windows, AmigaOS 4 and OpenBSD as free and open-source software. Wikipedia
Plot: Widelands is a free slow-paced real-time strategy video game under the GNU General Public License. Widelands takes many ideas from and is quite similar to The Settlers and The Settlers II. It is still a work in progress game, with development still required in graphics and bugfixing. 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