Ad hoc
A one-input game about the difference between explaining the data you have and predicting the data you will get.
Draw a loop around the filled dots.
A number in the corner says how well the loop describes the dots in front of you, and it updates as you draw. Redraw as often as you like. When you commit, a much larger set of new dots appears, drawn from the same source, and the loop is scored against them. The gap between the two numbers is the result, and beside it, what a simple boundary would have scored.
A boundary that explains everything you have seen will fail on what you have not seen yet. Nothing on the page says so; the result shows it in two numbers.
One set a day, the same for everyone, and one commit. After that, practice sets without limit.
WebGPU where the browser has it, and a Canvas2D renderer where it does not, so the game is whole on any phone. No camera, no account, and nothing leaves the machine.