The Daily Sudoku

One new 9x9 grid shows up each day, and the rules are the ones you already know: every row, column, and 3x3 box needs the digits 1 through 9 with nothing repeated. The Daily Sudoku keeps an archive of previous puzzles, so missing a day doesn't mean losing it — you can go back and clear it whenever you get around to it. There's no timer pushing you, which suits a slower, one-puzzle-a-day habit better than marathon sessions.