Rulehunt
Sudoku, but we won’t tell you the rule.
Every board hides one extra rule. The board refuses digits that break it. Read the refusals, test a hypothesis, name the rule — and record it in your bestiary.
Rulehunt is a paid-once puzzle game for iPhone: lessons, a daily hunt, a mystery casebook, expeditions and a bestiary of twelve rules. No ads, no subscription, no account.