The solver folder contains a C program to generate and solve Sudoku problems. It also has a nifty option to list every single completed Sudoku puzzle in an ordered way, though you may need a few lifetimes for it to finish. (It generates about 30000 puzzles per second on a single core on my laptop and there are about 10^21 Sudoku puzzles.)
The README.md file in the solver folder explains how the C program works.
All the code is FLOSS. See the LICENSE file.