Daily Anti Knight Sudoku
The extra rule
No two cells a chess knight's move apart may hold the same digit.
On top of the usual rules, a digit cannot repeat a knight's move away: two across and one along, in any direction.
Select a cell and every square it fights with lights up, knight moves included, so you can see the constraint rather than having to picture it.
It adds no new regions at all, only forbidden pairs, which makes deductions arrive from across the grid instead of along a line.
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.