common public license (cpl1.0) source for two command line
solvers has been posted at
http://www.research.att.com/sw/download/tgz/ast-sudoku.2006-01-24.tgz
even though it is open source there is a license handshake
for rationale see
http://www.research.att.com/sw/download/faq.license.html
sudoku is a 9x9 technique based solver
I stopped coding new techniques at x-cycles (~simple coloring)
sudocoup is an NxN sudoku/QWH (latin square) solver coded for speed
its a backtrack solver, but solves most 9x9 sudoku without backtracking
using a 1 level forward check
for a refreshing change neither solver employs dancing links