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.
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.