Daily German Whispers Sudoku
The extra rule
Along a line, neighbouring digits differ by at least five.
From a 4 you can only step to a 9. From a 5 you can go nowhere at all, so 5 never appears on a line.
That single fact does most of the work. Lines end up alternating between the low digits and the high ones, and once you place one digit the whole line narrows to a handful of options.
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 also a kropki sudoku, a xv sudoku, a greater than sudoku, a nonogram with hand drawn pictures, and 2048. All of them are on the games page, and the solvers for real objects are on the puzzle tools page.