FOSS games recommendations

Shattered Pixel Dungeon is my go-to roguelike.

I hear UnCiv is a very good Civilization clone.

Endless Sky has a mobile port on F-Droid. You fly a ship around, doing trade, missions, attacking pirates (or being a pirate). There are also a few storyline missions, many hours of fun and the game is still in development. There are some quirks on mobile but I put many hours into it, it's good fun.

Mindustry is also fun, and has many hours of potential. It's also a port of a PC game, this one works very nicely on mobile. It's sort of a Factorio (conveyor belts) tower defense game.

Puzzles is one of the best puzzle collections, humanity has produced.

As in, they're excellent puzzles and there's quite a number of them. They don't necessarily captivate with their visual fidelity or storytelling. 🙃

Can alternatively be played here: https://www.chiark.greenend.org.uk/~sgtatham/puzzles/

For a serious game I'd recommend UnCiv, imho the best adaptation of Civ to the mobile form, even counting official games. Very frequently updated.

For casual games, I like:

Lona: like Snake from old feature phones, but with circular motions. You'll understand it when you see it. Familiar and fresh gameplay at the same time. Difficult to master and keep beating your highest scores. Very addictive.

Vector Pinball: as it says on the tin, just an honest to dog, simple pinball. Many tables to choose from.

I'm also addicted to Poland can into space, which is a stupid game with bad gameplay, but fun nevertheless. :)

OpenMW - an open source implementation of the Elder Scrolls: Morrowind engine. It does require the data files from the original game though, so I guess not entirely FOSS.

Nonocross - a nonogram puzzles app with some default boards and a very simple design.

Pekka Kana 2 - an old wacky 2D platform with you commanding a rooster going from start to finish of every level.

SuperTuxKart - a classic by now, a complete parody of the original Crash Team Racing with characters being mascots from various projects and important elements of the Linux ecosystem.

(not on F-Droid) OpenRCT2 - a re implementation of the Roller Coaster Tycoon 2 engine. Free and open source, but requires the game's files.

Unciv and SuperTuxKart

PipePanic is pretty addicting.

RetroArch could also be worth a shot if you're open to emulation: https://f-droid.org/packages/com.retroarch/

Destination Sol is a 2D open world space arcade/RPG.

I have had fun with Egyptian Mouse Pounce. which is Egyptian Rat
Screw card game played against a cat.

Super Retro Mega Wars

Is a collection of games based on retro classics, with multiplayer.

Xeonjia a puzzle rpg where you are the newly choosen kid that must save the kingdom from the evil wizard. The main gameplay is trying to find the right path since when walking on ice you will continue to slide in that direction until you hit something. There is some light rpg elements with combat and it can be very challenging despite it's simplicity when combined with the slide mechanic and the tendency of enemies flee you.

Feudal Tactics found on f-droid. Extremely simple yet very fun, so many hours spent just conquering islands x3

Minetest and mindustry