Cryptex

A brass cryptex with one letter ring for each letter of a secret word. Type a guess and the rings click round to it. Each try marks every ring: the right letter in the right place, a letter that belongs on another ring, or one that isn't in the word at all. The marks use shapes as well as colour, so they read without it.

Words run from four to seven letters. The longer the word, the more letters each ring carries and the fewer tries you get: a four-letter cryptex has eight letters a ring and eight tries, a seven-letter one carries the whole alphabet and gives you six. Run out of tries and it jams, scrambling onto a new word. A guess has to be a real word, and a made-up one doesn't cost a try.

Every day brings one challenge, the same word for everyone on the same date, worked out from the date itself so adding words never moves anyone's challenge. The answers come from about 3,000 lock, puzzle and adventure words in frozen batches; a deploy stamps new batches with the first date that hasn't started anywhere in the world, so an update can never change today's word.

Cryptex started as one of the locks in my AR Escape Room, where a generated puzzle can end in a chest sealed with one, and clue scraps hidden around your room give away some of its letters. It became a game of its own on playallday.games, alongside the room's other mini-games.