Daily Window Sudoku
The extra rule
The four shaded windows must each hold 1 to 9.
Four extra 3 by 3 regions, offset from the printed boxes. Each window overlaps four different boxes, and the interference between the two sets of regions is where the puzzle lives.
Also called hyper sudoku.
Controls
Click a cell and type a digit, or use the pad. Space toggles pencil marks. Arrow keys move. Progress saves in this browser as you go, so you can come back to the same puzzle later today.
Solvable Without Guessing
Every puzzle here was generated and then handed to a solver that is only allowed techniques a person can use. If it could not finish the grid without a guess, the puzzle was thrown away rather than published. That also makes the answer unique, because every digit it placed was forced.
More to Play
There is a thermo sudoku, a killer sudoku, a nonogram with hand drawn pictures, and 2048. All of them are on the games page.