Which Do you know any open source games?

Battle for Wesnoth is fun, and there are many great add-ons available. I particularly recommend the SX, RPG, and similar maps, which give you a single strong unit each (single-player or multiplayer co-op) that advances and levels up, facing a huge horde.

https://en.wikipedia.org/wiki/Freeciv / https://freecivweb.com

https://github.com/yairm210/Unciv

https://en.wikipedia.org/wiki/Simutrans / https://www.simutrans.com/en/

https://en.wikipedia.org/wiki/OpenTTD / https://www.openttd.org

https://en.wikipedia.org/wiki/Widelands / https://www.widelands.org

https://en.wikipedia.org/wiki/Warzone_2100 / https://wz2100.net

https://en.wikipedia.org/wiki/OpenRA / https://www.openra.net/ https://github.com/OpenRA/OpenRA

https://en.wikipedia.org/wiki/Beneath_a_Steel_Sky

https://en.wikipedia.org/wiki/The_Ur-Quan_Masters / https://sc2.sourceforge.net

https://en.wikipedia.org/wiki/Cataclysm:_Dark_Days_Ahead / https://cataclysmdda.org

Pioneer Space Sim, it offers unlimited space exploration in a huge procedural generated universe. It's like a mix of KSP and No Man's Sky.

0 A.D., it has a gameplay like AOE with a theme of the 0 A.D. periods.

Xonotic, a fast-paced online FPS game, but it looks like the server don't have much players recently.

The Dark Mod brings you an experience of being a thief and sneaking through the darkness. It has a lot of community-made maps.

If you'd like, I have an open source-game called Dungeon Maze (https://github.com/raihankr/dungeon-maze). It's a maze solving game with 2d pixel graphics. It was made with vanilla HTML, CSS, and JS. Utilizing the HTML canvas, I didn't use any game engine library in the development.

https://en.wikipedia.org/wiki/List_of_open-source_video_game...

Freecol and Unciv are both open source