there is a project called xboard.
xboard is just only the graphical user interface to the underlying GNU chess engine.
Ya GNU chess engine consists an AI engine too than a simple min-max algorithm.And
to hack it's codebase,you needs a PHD in mathematics.
believe me that codebase is very complicated, and if you are not a patient code
reviewer to read and understand code first, please don't request svn access from
the project moderator or even submit any patches.
And it's hard but ppl are maintaining it.So its up to you to become patient and
read the codebase until you understand.