Preferably, apps that can be installed from F-Droid. APK recommendations are acceptable too.
Super Tux Kart and MineTest. Both are on fdroid and have amazing modding capabilities . I will say modding them is part of the fun too.
I’ve wasted too many hours on Shatter Pixel Dungeon.
You can get the source for OG Pixel Dungeon off GitHub, but there’s a maintened version on the F-Droid store (Shatter Pixel Dungeon). There’s some other free versions floating around too, not sure if they’re on the F-Droid store too, but I know they’re on the play store.
Flowit (Fill all boxes with the color of their border) https://f-droid.org/packages/com.bytehamster.flowitgame/
2048 Open Fun Game (2048 game with AI, Replay, History and other fun features, Open Source, no ads) https://f-droid.org/packages/org.andstatus.game2048/
Minesweeper - Antimine (A puzzle game where you search for all hidden mines. ) https://f-droid.org/packages/dev.lucanlm.antimine/
Shattered Pixel Dungeon (A roguelike game based on Pixel Dungeon) https://f-droid.org/packages/com.shatteredpixel.shatteredpixeldungeon/
Blockinger (Tetris clone) https://f-droid.org/packages/org.blockinger.game/
From what I can see Blockinger had its last commit 11 years ago. While it’s not on F-Droid (still FOSS though), my Tetris clone of choice is Falling Lightblocks. One super cool feature is 2 player competitive on one device using 2 game controllers.