Sudoku Classic

Standard sudoku with no theme or gimmick attached: a 9x9 grid, the numbers 1 through 9, and the same three rules — no repeats in any row, column, or 3x3 box. Pencil-mark notes are available for tracking candidate numbers in a cell, which matters once a puzzle gets past the easy tier and you need to hold a few possibilities in mind at once. It's a solid pick if you just want sudoku without extra modes or decoration around it.