YAsSS: Yet Another Stupid Sudoku Solver A C++ Program written by Moritz Lenz.
Algorithm:
described at http://moritz.faui2k3.org/yasss#algorithm
A german, more verbose project page is available here:
http://moritz.faui2k3.org/yasss
I hope I'll find the time to translate it soon.
To build yasss, you need a C++ compiler (tested with g++ 3.3.5-3). To generate the documentation, you need a2x from the `asciidoc` package (at least if you are using Debian ;-)), asciidoc and xsltproc.
Although file gui.cpp contains a first attempt to create a gui using gtk, you should not try to use it. It doesn't work. Period. Propably it will never work...