Side by Side (Game)

You enjoy Sudoku, but you’re up to something new? Here is what you are looking for!
Side by Side is a fascinating puzzle based on a few very simple rules.
In a 6x6 (or larger) grid, you start off with a few given numbers.
It is your job to fill in all of the grid’s boxes with any of the numbers 1 to 4 or an X. A number indicates how many of the directly adjacent boxes also contain a number (i.e., not an X). Further, two directly adjacent numbers must not be identical.
Features:
- more than 2000 puzzles
- 9 different grid sizes
- three difficulty levels
- game play hints
- convenient undo feature