Recomended software for 2007.
There are several chess playing programs on the market and most save games in pgn format. PGN is the Portable Game Notation format used by most websites and chess database software. Chessbase or cbf format is a second choice and is strongly recomended for players who really want to improve their game. By years end all of the thinkchess lessons will be available in this format. Below is several links to recomended chess software sites.