Sudokoban

Two puzzles welded into one, and the name says which: a sudoku grid you solve by pushing, box by box. Numbers one to nine leave a hint in a cell, zero erases it and H asks for help on the cell you are standing in — so the usual pencil-marking habits of sudoku are built in rather than kept on paper. Backspace rewinds a few moves on the easier settings, which is a kindness the harder ones withdraw.