Chomp
In the game Chomp, two players begin with a grid. The first player chooses any size square and covers it with blue. The second player chooses any size square and covers in red. The two take turns in this way until one of them is forced to remove the last square. That player loses.
Although I prefer to play the winner gets the last square...
Adapted from Paul Halmos, Problems for Mathematicians, Young and Old, 1991
Futility Closet reminded me of it: https://www.futilitycloset.com/2022/06/13/square-meal/
You can zoom in or or out to make a shorter or longer game, use the reset icon to make a new board.