From Media Division:
SparkChess is an excellent way to get better at chess - learn the proper rules (including the elusive en-passant), practice openings, test strategies, use the board editor to recreate famous positions via FEN strings, replay famous games, import/export via PGN and let the computer help you. With four levels of difficulty and a behavior modeled to make human mistakes, this is a fun game to play, not a frustrating one. With the multiplayer feature, you can put your skills to the test against other players like you.
SparkChess has won many awards and it was featured by Google, RIM and Adobe for its cross-platform capabilities. You can download SparkChess for PC, Mac, iPad, Android and Blackberry Playbook.