Ultra Sudoku

Varying types and difficulties of sudoku.

Would be perfect if it had a notes feature and some more background themes

missing essential functionality such as marking potential numbers for a square. All you can do is set the number for a square any you have to keep conflicts in your head as you play which makes this version far inferior to every other sudoku I've ever played.

it always gives false, unsolvable always gives invalid grids and broken puzzles that are logically unsolvable

Pros: Free Cons: Can't add notes, can't use numpad, can't reset board if you make an error. Also, I don't know if I just missed it somewhere but I couldn't find out how to undo a move If I ever made a mistake. The amount of times I had a miss click or fat fingered on free spaces was incredibly irritating when playing difficult and large puzzles. Without a notes feature to keep track and no "known to me" undo button, I was also keeping track of all the errors I placed on the board mentally. Still enjoyable because it's Sudoku but I'm ready to try a different Sudoku and say goodbye to Ultra Sudoku permanently.

Sudoku puzzles are great and always good for a quick break. The various versions besides the standard one are also well-designed.