This tool written in C uses the Backtracking algorithm to solve Sudoku puzzles.
The idea was born by participating a coding challenge of a German internet forum.
https://www.coding-board.de/threads/coding-herbst-die-coding-board-de-coding-challenge.39297/
So it's rather made for fun. However, this code won in terms of speed.
Unfortunately, the initiator of the contest has passed away in the meantime. R.I.P. Benjamin.