HoDoKu is a Sudoku generator/solver/analyzer. It has many human-style techniques (singles, subsets, LCs, fish, wings, uniqueness, coloring, chains, and ALS) and a powerful analyzer (manage multiple solutions for one Sudoku).
Python Sudoku Solver takes a Sudoku unsolved puzzle, e.g. read from some text file, and tries to solve it. It uses Python curses to display a very simple UI.
A Trac appliance that is easy to use and lightweight.
A file transfer client.