0AD. Similar to Age of Empires

If you like an RPG, Diablo style, there is also FLARE (Free/Libre Action Roleplaying Engine)

mindustry

Lichess.org for online chess, or (most private of all) a physical travel board if you’re with a friend who wants to play. Lichess isn’t very private but definition though. Not sure why you asked in c/privacy? Anyway what happened to reading a book on a bus trip?

Oh try universal paperclips if you haven’t. 5 hours is about right for finishing it. That’s pretty private.

Anuto TD and Breakout 71 are good time killers on the phone. Open TTD if you are into sims and Cataclysm: Dark Days Ahead if you want post apocolyptic turn based survival horror rougelike. There are also quite a few RPG fangames based on Lisa the Painful.

I time travel with unciv. This is how I once survived a 15 hour long haul flight.

Doom is always great. FOSS up to Doom 3, but you still need the full games for the assets. If you don’t have them there is still Freedoom. And The Dark Mod is a great free Thief like game on the Doom 3 engine.

Battle for Wesnoth, if you’re into that kind of thing.

Don’t know what you are into, or playing on but I’ve been enjoying endless sky recenty:

https://endless-sky.github.io/

I usually turn to shattered pixel dungeon

Install Warzone 2100, start poking the game files, adjust various numbers and see what happens. Give your cannons massive range, make every unit super cheap to manufacture or whatever. Your imagination is the limit. Play the game however you want. The game itself is good, but hacking it is just so much more fun.

friday night funkin is surprisingly apache

Balatro