Sudoku Soft Book

Sudoku Soft Book is an original sudoku game that offers three game variants. The traditional one, in which you must fill the empty spaces in a way so that each column and row contains the digits from 1-9; the Killer sudoku, in which the squares are grouped by dotted lines and all the digits of the squares must sum the number that appear in one of them; and finally, the Comparison sudoku, in which you must guide yourself with the symbols that appear in the squares indicating which has the largest number of the two squares.

The three variants offer only one size (9x9), but they all offer multiple difficulty levels. The numbers are entered using the keyboard and you can use either pen, if you are sure of the answer, or pencil, if you are not. Once you finish the puzzle, you can easily check it. You can also restart a puzzle whenever you want and reveal the answer in case you get tired of it. Unfortunately, it doesn't allow you to save or print a puzzle, and you cannot create your own sudokus. It also lacks hints to help you in case you get stuck.
In short, Sudoku Soft Book is a wonderful game for experienced sudoku players because it offers two additional challenging variants, but still lacks a few features for beginners and some others that would definitely make it more attractive.