Solves sudokus.
Works by performing a depth-first search, filling in the blank values and terminating the branch when an inconsistency is found (duplicated numbers appearing in a row, column or 3x3 box).
sudoku.py is an implementation of this in Python, index.html is a Javascript implementation that you can actually use here.
As the name suggests, the folder AndroidApp contains an implementation of this in the form of an Android App.