Decodex

Decodex is a cryptogram puzzle made by Áron Csatlós, playable on the web and in an iPhone and iPad app. The website's daily challenge is a quotation encrypted with a simple substitution cipher: each letter in the quote has been replaced by a different one, consistently, with spaces and punctuation left as they are.

You click a code letter and type the letter you think it stands for, and it fills in everywhere that code letter appears. The author of the quote is shown at the top as a first hint, which can tell you the era and the kind of words to expect. If you are stuck, a small set of helps can each unlock a letter, and you can surrender if the quote beats you. A timer runs while you play, and the game keeps a streak of days solved.

Each day's quote is dated, and a Past Games page lets you go back to earlier ones. There are also Campaigns of themed puzzles, and the app has its own daily puzzle that differs from the website's, plus app-only campaigns. The site carries ads, which donors can switch off with a code. The iOS app adds more than 50 quote categories, stars per solve and a premium tier with hint packs. It suits players of the newspaper cryptoquote and anyone who liked Decipher or Cyphr.