Perl6-Sudoku is a project mainly written in Perl, it's free.
Perl 6 class for representing (and later solving) Sudokus
This is a Sudoku class and solver, designed for flexibility (but for example the constructors aren't yet sufficiently flexible).
A simple solving algorithm is implemented, but it doesn't solve all possible Sudokus yet (in fact, it doesn't fully solves the one I tried with).
License: Artistic License 2.0