My favorite is the Natural Number Game: https://wwwf.imperial.ac.uk/~buzzard/xena/natural_number_game/ https://wwwf.imperial.ac.uk/~buzzard/xena/natural_number_

My favorite is the Natural Number Game: https://wwwf.imperial.ac.uk/~buzzard/xena/natural_number_game/ https://wwwf.imperial.ac.uk/~buzzard/xena/natural_number_gam... A series of levels where you prove ever-more-complex theorems in Lean, gaining each proved theorem as a tool to use in proving further theorems! Best puzzle game I've played in years.