SudokuExplainer Java (Swing) GUI explains how to solve Sudokus
Keith Corlett's open-source SudokuExplainer explains ANY Sudoku puzzle, and generates human puzzles. It's a Java (Swing) GUI based on DIUF SudokuExplainer by Nicolas Juillerat (rewritten for speed) with all hinters from HoDoKu by Bernhard Hobiger, plus a few from sudopedia.com.
SE explains a simplest possible solution to ANY Sudoku puzzle. It's pretty fast.
This is no Sudoku solver, but "explainer". It can guide you with logic through the solving process. Not only 9x9 grids: MxN, samurai or any layout you can describe with the board editor! Now with a great GUI! Manual, tutorial, examples...