[Dave Peck's Go]
http://go.davepeck.org
"Play Go online with your friends. It’s fun, easy to get started, and free!
This site was built by Dave Peck and other members of the Go community."
Cult of Mac - Learn New Humility: Play "Go" On Your Mac
http://blog.wired.com/cultofmac/2006/12/learn_new_humil.html
"It's sort of like playing a really evil version of Othello that requires the use of more strategies and gambits than chess."