Sudoku Sensei is not a Sudoku solver, but an "explainer". It can list the logical steps taken. It can generate new Sudokus and rank their difficulty. It supports not only 9x9 grids, but MxN, samurai, or any layout you can describe with the board editor. It has a GUI, manual, tutorial, and examples.
Petals on a Rose Game is a computer version of the famous riddle/puzzle game called Petals on a Rose. It is rumored that Bill Gates was stumped by it for two days. It's usually played with a group of friends and a set of 5 dice. The game master rolls the dice and tells everyone the answer. This computer version of the puzzle works similarly, only in this case the computer plays as the game master. There is no source included because that would give away the answer. The binaries were made as universal as possible.
YasSS (Yet another (simple|stupid) Sudoku Solver) is a Sudoku solver for the command line. It solves any Sudoku puzzle and generates Sudoku puzzles. It can calculate the number of solutions, print a difficulty rating, and generate a canonical form for a puzzle. It also provides a curses interface for playing Sudoku.