This is a very simple implementation of "Reversi" (a. k. a. "Othello") board game, which requires no registration. No, seriously, no registration whatsoever! Just introduce yourself by whatever name you like and get a "secret link", send it to a friend by e-mail/IM, and he/she can join the game.
I wrote it after tryig to find an online site to play reversi with some friends and getting overly frustrated by what I found. All of them (all of them!) required a painstaking registration process (3 pages, 20 fields each, all mandatory, e-mail confirmation required) just to discover that there's either no reversi, or I can't play it against a particular opponent, or I have to buy a premium account and whatnot.