Flappy Flap Cat by Adam Carter
Simple, yet frustrating. No in-app purchases, no "lives" where you run out and then have wait to refill, just tap, play, and when you lose (which you will), just start again and try to beat your high score. Or try to beat your friends highest score, if thats your thing.
Works on all iPhone screen sizes, as well as iPads.
Don’t get mad at me if you break your shiny new iPhone X by throwing it across the room in anger and frustration.
Enjoy.