Turn two cards over. If they carry the same shape they stay up; if they do not, they go back down after a moment and it is on you to remember where they were. Clear the board in as few moves as possible.
The score is the number of moves, with the clock only as a tie break, because this game is about remembering and a player who taps faster has not remembered better. A perfect round is one move per pair.
Tab and Enter work through the whole board, N deals again, M mutes, F is fullscreen.
Tap a card to turn it over. A tap while a wrong pair is still showing turns them straight back rather than being ignored.