Mobile games usually get a bad rep as they’re usually asset flips and/or MTX-ridden and/or ad-filled, etc., and I’m sure this is actually the case for most games on the app/play store. But are there any ones that are actually good, maybe just something to pass the time with?
Free, ad-free, open source phone games
Unciv: Civilization V clone that runs on a potato; a grand 4x strategy game. It seems pretty mechanically complete and has a lot of content. Easily modded. (Graphics may not be to everyone’s taste)
Simon Tatham’s portable puzzle collection: Mathematically inspired Puzzle games with a lot of customization and reasonable interface. This includes classics like untangle (graph planarity) and solo (sudoku, but generalized). I personally really enjoy Tower, and hadn’t seen it elsewhere (and like 15 more games besides).
Chip defense: computer science themed tower defense. By the power of Turing, Noether, and Knuth you can strike down malicious packets attempting to corrupt your CPU. Good content, fun towers and educational bonus material, and I think it looks rather good. (Minor gripe/warning: early levels are optimally played with a lot of tapping that is not very ergonomic; this drops off after the first few levels.)
Honorable mentions (not FOSS, but still free, MTX free, and no ads beyond fishing for a rating). Higgster’s game compendium: collection of games in a consistent and pleasing artstyle. Includes things like solitaire, wordle, binaro, and mastermind (20+ games total, several more have been added in the last year). This is really very well done, give it a look!
Flocks: Sliding puzzle game with excellent graphics and animations. Lots of levels, introduces new mechanics regularly, and easy to pickup or put down. I quite enjoy everything Robert has made, recommended!
Piggybacking onto this (all of these are FOSS):
Endless Sky is a 2D sandbox space sim. It’s a spiritual sequel to the old Escape Velocity: Nova, and has very active development.
Feudal Tactics is an extremely simple strategy game that can nonetheless be quite hard.
Battle For Wesnoth is a whole-ass fantasy campaign turn-based strategy game that has been ported to mobile. Think Warcraft but turn-based.
Arx Libertatis is a port of Arx Fatalis, a first-person RPG. This one is still on my list to try out, but it looks interesting.
Feudal Tactics looks like a Slay clone. My favorite Slay clone is Konkr, playable in a browser.