Plot: The GNOME Games collection is a collection of about 15 puzzle video games that is part of the standard free and open-source GNOME desktop environment. They have the look and feel of the GNOME desktop, but can be used without it. Wikipedia
Plot: GNOME Chess is a graphical front-end featuring a 2D and a 3D chessboard interface. GNOME Chess does not include a chess engine of its own, so to play against the computer a third party chess engine must be present. Most Linux distributions package GNU Chess as the default chess engine with it. Wikipedia...
Plot: gbrainy is a free and open brain teaser game for GNOME designed for use in education. It is licensed under the GNU GPL. The game was written in C# and has since been ported to the Sugar graphical environment, to Microsoft Windows. 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