So please tell me the games you know or maybe created yourself.
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://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
Dungeon Crawl Stone Soup is great if you enjoy roguelikes. It's designed to avoid a lot of the manual tracking needed in other roguelikes; for instance, you can search for where you left an item, or hit one key to explore unvisited areas of the current floor until you see anything unusual.
Hedgewars is a clone of Worms, if you're familiar with that.
Shattered Pixel Dungeon is fun, and available on mobile devices.