There is very little to tell about this program. It is just an attempt to make a program which solves Sudoku puzzles.
See the sources. I just hope it is a useful demo. Useful as in you can learn something from it.
The application can be found on the Lazarus CCR Files page.
If you run the program you will see a grid, and two buttons. If you press the "Fill" button, you are able to edit the grid and place the numbers in the grid according to your puzzle.
When you are finished entering the digits press "Solve" and the grid will be filled with the solution.
The programs solves all Sudoku puzzles that can be solved by logic. It will not solve the puzzle where you need to guess for a solution.
So it follows these rules (taken from WebSudoku):
The rules of Sudoku are simple. Enter digits from 1 to 9 into the blank spaces. Every row must contain one of each digit. So must every column, as must every 3x3 square. Each Sudoku has a unique solution that can be reached logically without guessing.