Sixy Sudoku puzzles bring a whole new dimension of logic, making a 6 x 6 possibly even more fun than a 9 x 9 Sudoku! There is no plain hard work, just a lot of logic and insight.
Peter Ritmeester, founder and owner of PZZL.com, is the inventor of Hyper Sudoku where four gray regions also contain 1-9.  By applying this idea to 6 x 6 Sudoku, an additional level of logic is created.
Pocket Posh Sixy Sudoku Easy to Medium Puzzles
features a foreword, an extensive how-to-play section, 200 easy to medium puzzles, and complete solutions at the back.
The rules: insert the digits 1-6 just once in each a) row, b) column, c) bold outlined area AND d) in each white and gray rectangle.