Don Woods' Freecell Solver
This is the source code for the famous Freecell solver by Don Woods. It is basically 4 different solvers for four different Freecell variants which are using a very similar algorithm. Maybe it is possible to abstract the game rules and integrate all of them into one solver.
The copyright notice says:
(c) Copyright 1993, 1997, Donald R. Woods. Shareware: Right is granted to freely redistribute this source provided this notice is retained.
Note that a more optimized derivative of this solver (for Freecell alone), which was modified by Wilson Callan and Adrian Ettlinger, is available as part of Freecell Pro. FC-Pro is an open-source GPLed program, whose source code is available.