Crux

Normal sudoku is 1 to 9, once per row, column and box. Crux keeps that and adds a constraint on top. Killer cages: the digits in a dotted cage add to its little number and never repeat. Thermometers: digits increase from the bulb to the tip. Whispers: neighbours on a green line differ by at least five. Arrows: the circled digit is the sum of the cells along its arrow. Anti-knight: no two cells a knight's move apart share a digit. Non-consecutive: touching cells can't be 4 and 5.

Early puzzles use one extra rule. By the back half you get two or three at once, which is where it stops being sudoku with decoration and starts being its own thing. 120 puzzles in total.

Controls: tap or click a cell, then a number. Pencil marks, undo and a check button are all there. It saves your progress, so you can leave a puzzle half-done and come back.