It's bit hacks all the way down!
This is an ongoing project that emphasizes performance.
Most of the fun stuff happens in {src, include}/player/Computer/, where Alpha-Beta search governs the Computer player's decision process (take a look at src/player/computer/search.cpp for a Minimax/Alpha-Beta review).
The sub-directories of include, src, and test all mirror each other. The first-level directories can be summarized as follows:
board: Contains everything needed to play the game; Square, Piece, Board, etc. are all maintained here.
game: Move generation and rule enforcement. Moves executed through the functions here are subject to the rules of chess.
player: Contains a basic Human player and the brains of a Computer player.
util: Various tools used throughout the codebase.