Where to Play Chess : Introduction
Computer and network technologies have revolutionized the royal game. There are now more ways to meet and play opponents than at any time in the long history of the game.
Little ChessPartner (thechesshaven)
Play against a variant of software from Lokasoft. Use 'Settings' to control the computer's search depth or calculation time. Source is also available.
Thinking Machine
'Explores the invisible, elusive nature of thought. Play chess against a transparent intelligence, its evolving thought process visible on the board before you.'
WebChess (chess.delorie.com)
Play online against a computer. ('Welcome to the world of GNU Chess, linked to the Web.')