Kelly

Hold to bet. Let go to flip.

A bar fills while you hold, and the share it shows is the share of your bank you put on a coin that wins 60% of the time. A small cut is taken from the bank after every flip. The bank is the one number on the screen, in words, the way a clicker game says it.

Nothing gets harder. The coin, the bar and the cut are the same at flip 1 and flip 1000. Bet too much and one losing streak ruins you. Bet too little and the cut bleeds you out. Between them, a narrow band grows without end, and the game never says where it is.

A second bettor plays the same coin, unseen, putting 20% on every flip. The run ends when your bank is gone, and the card shows where each of you ended, on one axis: yours going up and through the floor, and the white line that lived.

Canvas2D, so the game is whole on any phone. No camera, no account, and nothing leaves the machine.