Cabinet 07
Chess
One board, two people, one device. Turning the board suits two people sharing a phone; it also mirrors every square each move, so pieces jump rather than slide. Nothing is sent anywhere and nothing is rated.
Create a room and send the link. The board lives on the server, so neither side can move out of turn or invent a move the rules do not allow. Finished games move both players on the Elo ladder.
Your rating
Moves
Full rules: castling, en passant, promotion, checkmate and stalemate, plus the draws that are easy to forget, threefold repetition, the fifty move rule and dead positions with too little material to mate. Drag a piece or tap it and tap where it goes. Pass and play runs entirely in this page and sends nothing anywhere. Against a friend the match is refereed by a server that owns the board: it decides whose turn it is and which moves are legal, so a tampered page can ask to move a pinned knight or castle out of check and simply be told no. That same server computes the Elo, from the result it saw itself, which is the only reason a rating here is worth anything.