Chess Rating Calculator - will calculate your rating; easy to use.
IECC Chess Rating Calculator - written by Brad Coulding for rating IECC games.
MailChess an e-mail chess program, similar to ECTool, and some find superior because it can keep track of tournaments
Scid - a free chess database application for Unix/Linux and Windows operating systems. Version 3.5 available as of December, 2003
Macintosh
ExaChess is a freeware database program
MacChess is a freeware chess-playing program used by many
Sigma Chess is a freeware chess-playing program
SmartChess is a commercial database ($89)
ChessPuzzle 2 is an easy to use puzzle solving game, with over 6000 puzzles and a powerful built-in chess engine