Description from the designer:

Solitaire Gin Rummy is a solitaire card game that can be played anywhere because you hold all the cards in your hands. It was described in Games Magazine, June 1998. Unlike other solitaire card games, which require the cards to be laid out on a flat surface, Solitaire Gin Rummy can be played in line at the grocery store, in a theater while waiting for the movie to begin, on a windy beach or on the bus. If you are interrupted, you can bundle the deck into your pocket without losing your place in the game, and take it up later.

The rules are designed to be as close to Gin Rummy as possible. Your opponent is the joker. Your goal is to "go gin" before the joker appears.

Place one joker in the deck, and remove the other joker. Shuffle the deck thoroughly. Deal yourself ten cards. Hold them in one hand, and either set the rest of the deck, face down, beside you, or hold it face down in your other hand. This is easier to do if you use miniature cards. If the joker appears in your hand, you can either say you lost that hand, or you can just reshuffle and start over.

Draw the top card from the deck and put it in your hand. Discard one card from your hand, so that you still have ten cards in your hand. Place the discarded card on the bottom of the deck. The goal is to form "melds" in your hand. A meld is a set of three or more cards that are either all the same kind (eg. all threes) or form a numerical sequence all in the same suit (a straight flush in poker.) If all the cards in your hand are in melds, you have "gin" and have won the hand. If the joker appears before you go gin, you lose.

Optional scoring and knocking

If you would like to make the game more like real gin rummy, you can keep score for several hands. The first player (you or the joker) to get 100 points wins the game.

If you have a gin hand, turn over the cards in the deck one at a time until the joker appears. The number of cards you turn over is your score.

If the joker appears before you have a gin hand, add up the values of cards you have in your hand that are not in melds, counting number cards at face value and court cards as ten. The total is the joker's score.

If your hand contains ten or fewer points in unmelded cards, you may "knock". Stop play and figure the two scores as described above. The one with the higher score recieves the difference in scores. For example, suppose you knock when you have a three and a five unmelded in your hand. Your hand counts eight points for the joker. You count the cards in the deck until the joker appears, and there are ten cards, which counts as ten points for you. Instead of giving ten points to you and eight to the joker, just give yourself two points, (ten minus eight.) If you scored and the joker scored ten, you would give the joker two points.

If you knock and the joker turns out to have the higher score (that is, there are more points in unmelded cards than there are cards above the joker in the deck), the joker receives 25 bonus points for "undercutting the knock." If you get gin while playing with this rule, you recieve 25 bonus points.

I usually don't keep score; it's more fun for me just to play a quick hand. But because there's so much chance involved in where the joker will be, keeping score over several games would give you a better idea of how well you're playing in general. You could have a goal of improving your average over time.