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 Enigma continues to be very popular as an open source multi-platform derivative of Oxyd now that Oxyd is no longer maintained.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: 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: 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: GLtron is a 3D snake game based on the light cycle portion of the film Tron. The game is free and open-source software and has been ported to many mobile and non-mobile operating systems such as Windows, MacOS, Symbian and Android over the years. 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