Jotto is a two player word game which is similar to "Mastermind". Rather than using a pattern of colored pegs, the hidden target is a five letter word.
Both players choose a five letter word, which they write down on a pad of paper, kept hidden from the other player. Alternately, each player then challenges the other with a five letter word. The challenged player must report how many letters in the challenge word are matched by the player's hidden word. Play ends when one player guesses the hidden word of the other player.
Note that no information about the placement of the letters is available. Thus, it is possible for me to know all your letters, and yet not win. For instance, I may figure out that your word has the letters "PTNAI" and guess "PAINT", but even though you report five "hits", I don't win because your word is "PATIN".
A sticky problem that should be resolved before playing is the question of doubled letters, both in the hidden word and in the challenge words. For instance, suppose your hidden word is "CLASS" and I challenge with "PASTA". Should you respond with:
One of the many advantages of Jotto over Mastermind is that many desirable challenge words aren't legal. They have to be words. So, as in Scrabble, you have to struggle to come up with a word that uses some of the letters you need to use.
You might try a variation in scoring challenge words, which is to double the score for each letter that is in the right position. This makes it harder for your challenger (and you, as well!) to determine the meaning of a response like "3", which now could mean three right letters, each in the wrong spot (which tells you something) or two right letters, one in the right spot.
You may have run across this game under the name "Ghost". I believe James Thurber wrote an article about it under that name.
Dedicated to Herb Wasserberg, who showed me this game, wherever he may be hiding!