Simon Tatham's Puzzles

Any of the Pixel Dungeon games.

I have quite a few recommendations. They are not quite non-freemium since they are free, but if your reason to prefer non-freemium is to avoid ads and in app purchases, then none of these games have them. They are all also open source and the link I provided below will be for their respective F-Droid version (note: some of these games are not available on Google Play Store):

• Simon Tatham's Puzzle - A collection of many puzzle games ported to Android. The puzzles include Minesweeper, Net, Sudoku, and more.
• Simple Solitaire Collection - As the name says, it's a collection of card-based Solitaire games.
• Simple Brick Games - A game that imitates very basic handheld with very small pixel count. Games include tetris, breakout, and more.
• 1010 Klooni - A puzzle game where you have to use various shaped blocks to fill an entire horizontal or vertical line.
• Tower Jumper - This is a clone of a popular android game in which you move a jumping ball and try to reach the end of a tower avoiding the obstacles.
• Ball2Box - A puzzle game about shooting a ball into the box.
• Anuto - Another ugly tower defense.

This particular game requires far more attention and strategy than the ones listed above, but it can be played once every few minutes if you constantly save and reload (just don't play online):

• Unciv - 4X civilization-building game, similar to Sid Meier's Civilization series.

Vector Pinball

Everything by Bart Bonte.

Smash Hit is a very chill game. You throw balls to smash glass, levels get progressively harder as you go along (but still chill)

Brotato.

Sherlock Zen is a logic puzzle game that looks like dos shareware from the win 3.1 era.

The previous version was one of the first android games I ever installed, I played through the free levels a couple of times but never bought the unlock.

I thought about it recently when doing a grid logic puzzle in a magazine I bought at the airport and went looking for it. I was sad that it didn't seem to exist anymore and eventually went down a rabbit hole and found the creators website which gave me huge nostalgia. He is also active on mastodon. So I bought the new version finally and have been thoroughly enjoying it!

Chess Puzzles or Bullet Chess on the Chess.com App

• Alto's Adventure / Alto's Odyssey (has options to buy upgrades but none are required, there is no "win" condition)
  • There is a clone on F-Droid called Lato
• Lyne
• Golf Peaks
• Shortyz Crosswords

Pathos Nethack - An elegant adaptation of the classic Nethack procedurally generated dungeon crawler for mobile devices.

It actually solves a lot of frustrating problems with Nethack.

Much better on mobile than the official Nethack port.

Egg, Inc is really good.

It has some freemium qualities. But you can get hundreds of hours out of it by purchasing the "pro permit" and nothing else.

The game has no ads (err, you can choose to watch a single ad to get an 8 hour bonus)

I play sand:box, it's free without ads, but if you want some extra materials to play with you have to pay a dollar for premium, i never get bored of it.

axolotl rush with ehter firewall like the one in calyx os or with Adblock dns

To Arms is a free deck builder. It's not pretty, but I love it. It's also free

Solitairica is a fun RPG twist on solitaire. It's a couple bucks

Hungry Cat Nonogram. Free version has ads but contains all levels.

Desert Golfing. I've been playing this one for almost a decade now, probably got my $2 worth.

I don't normally game on mobile but I occasionally play AlphaBetty. It's like a bubble pop/scrabble hybrid game

Any of the Papa's games from Flipline Studios. They cost a few dollars each, very casual singleplayer without any ads or IAP prompts.

Sokoban! It is the classic puzzle game. There are many versions, I prefer the one on F-Droid.

Very Little Nightmares is cool. I personally also like Dungeon Village 2.