Autosave — Your current game is saved in your browser after every move. If you leave the page, you'll be able to resume exactly where you left off. Saves are kept for 7 days.
Shared stats — Your stats are shared with the Classic Sudoku 9×9 page. They're stored locally and never sent to a server.
Daily puzzle — The 📅 Today button loads the same puzzle for every player on a given day. It changes at midnight.