These links in one way or another have either helped me create and build or are important to GregsChess.

These are articles on different chess save game file structures:
Wikipedia - PGN - Portable Game Notation
Wikipedia - FEN - Forsyth–Edwards Notation
Wikipedia - X-FEN - Extension for Forsyth–Edwards Notation
Wikipedia - .PDN - Portable Draughts Notation
Wikipedia - .SGF - Smart Game Format
Internet Chess Club - Smith Notation

Human save game systems:
Wikipedia - AN - Algebraic chess notation
Wikipedia - Descriptive notation
Wikipedia - ICCF numeric notation
Wikipedia - GBR code - Guy–Blandford–Roycroft code

Chess Variants:
Wikipedia - Chess Variants