Expert Sudoku Book Stress Free is a free Sudoku game developed by Boy Howdy Technology LLC for iPhone users. The game consists of 160,000 Sudoku puzzles that are divided into four difficulty levels - Easy, Medium, Hard, and Evil Sudokus. The game has four different types of Sudokus to try, including X Sudoku, Hyper Sudoku, Jigsaw Sudoku, and Samurai Sudoku.

The game has a beautiful and easy-to-read interface with a fast and intuitive dual-keypad input system. The horizontal and vertical guidelines make it easy to look at your current row and column. The game also features an auto-highlight function for other cells with the same number and cells that have a visible conflict.

Moreover, the game includes a hint function and a check your work function that allows you to spot any problems. The game also saves your progress automatically, so you can take a break and come back later without losing your progress. The game is also customizable, with the option to disable sounds and listen to your own music while playing.

Overall, Expert Sudoku Book Stress Free is an excellent Sudoku game that offers a wide range of puzzles and features to keep you entertained. Download it now and start having fun!