Most Sudoku apps treat a hint as a lookup: you're stuck, you tap, a digit appears. Sudoku by Bonendo treats a hint as a short lesson with a proof behind it.
Look along this cell's row, column and box: between them they already use eight of the nine digits.
Ask for a hint and the app finds a step a person could genuinely have made, points at the cells that matter, explains why they force the conclusion, and only then offers to place the digit. You choose how far down that ladder to go. Hints are unlimited, free, and never held against you.
After every solve, a review card lists the techniques the puzzle needed, easiest first, and marks the ones you read a hint about.
Eleven techniques from Last Empty Cell to Swordfish, XY-Wing and Simple Colouring, each with a worked example on a real board and a practice mode.
A dated puzzle every day, a calendar of the last year, and a streak that forgives one late solve a week.
Limited-time events with bronze, silver and gold medals, and Game Center rankings against other players. Every puzzle you solve while one runs counts.