I rarely play games anymore, but on the rare occassions I do, I prefer https://en.wikipedia.org/wiki/Freeciv / https://freeciv.org

It's playable in all sorts of ways (against AI, Humans, real-time, long-turn) via https://www.freecivweb.com in the browser, without having to install anything.

There are many different rule-sets now, the most modern and balanced seems to be

https://freeciv.fandom.com/wiki/Multiplayer_II_Dragoon_Summa...

https://freeciv.fandom.com/wiki/Design_Log.mp2d

https://freeciv.fandom.com/wiki/Multiplayer_II:_Dragoon,_Gam...

Be warned, it can be a massive time-sink!