OpenTTD

“OpenTTD is an open source simulation game based upon Transport Tycoon Deluxe.”

5 hours is enough to get addicted to this crack…

mindustry

maybe try out pico8

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

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

0AD. Similar to Age of Empires

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

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.

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

If you are fine with VNs (visual novels) as games, there is Katawa Shoujo. There is a “remastered” version of it in F-Droid for android: https://f-droid.org/packages/sh.fhs.ksre/

If you are going to use a laptop (linux natively supported): https://www.katawa-shoujo.online/download

friday night funkin is surprisingly apache

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.

fgunz.net

So… I understand OP asked for FOSS games, so here is 1 suggestion : HyperRogue, an SDL roguelike in non Euclidian space https://www.roguetemple.com/z/hyper/

… but I mostly come to argue that in this specific case, namely short lived entertainment, FOSSness is IMHO not as important as elsewhere. I am NOT promoting closed source software here but I want to highlight the fact that unlike an OS or a DE or any software recurrently used within that setup, e.g. a video editor or a script, a game is typically not combined with other tools and is supposed (most games at least, not all!) to be used “as-is”. Namely that one typically (counter example, Minecraft, with its countless FOSS alternatives) play the game, finishes it and moves on. One does not have a game being a building block or a workflow nor do they finish it and… keep on playing it (counter examples here being online games, due to competition and collaboration, user generated content).

So yes I understand the desire to want to keep a system “pure”, namely rely entirely on FOSS software but I for example enjoyed Baldur’s Gate 3 last year or Elden Ring at the moment despite them NOT being FOSS precisely because… they are not central to my workflow, or the way I think. Do I wish they were FOSS? Yes, absolutely! Do I wish all the content I consume, from music to books, would be DRM-free at least? Totally and that’s why I typically look for this kind of content first. Yet… if there is one place where I’m more leniant than elsewhere, it’d be games.

My 2 cents, anyway HyperRogue is cool! ;)

TL;DR: FOSS games are near but arguably when it’s for a short period of time, in some cases depending on your worldview, maybe non FOSS games can be acceptable.