Stillgrid

Stillgrid is a modern, Calm sudoku platform offering multiple puzzle variants including Classic, X-Sudoku, Jigsaw, and Killer sudoku. Features technique-graded difficulty levels to match all skill levels, It's free and open source (MIT), with no ads, and plays at 6×6, 9×9, and 16×16 grid sizes.

Perfect for puzzle enthusiasts looking for a clean, accessible way to enjoy sudoku on mobile devices or the web.