Gin Rummy
Gin Rummy 
This is a card game for two players ( 3 or 4 can play)
Cards.
The normal full pack of 52 cards is used (no jokers), card ranking from Ace (low) to King (high) ranking of suits is irrelevent.
Objects of the Games.
To be first to knock by laying out all or most of one's cards in melds.
Melds-A meld is three or four cards of the same rank, or three or more cards in suit and sequence.(Ace low only)
examples of melds 
Play.
Highest cut deals. Dealer deal each player ten cards, in ones. Turn the next to start the wastes-pile (the faced top card of the wastes-pile is called the upcard), and stack the rest of the cards face down (known as the stock). Non-dealer (elder) may take the upcard or pass. A pass give the dealer the same option . If both pass, the non-dealer must take the top card of the stock into hand and make one discard to the waste pile. If you take the upcard you may not discard it at the same turn.Wastepile must be kept square up (optional)
Knocking-A player may knock only if the total face value of unmelded cards (deadwood) left in his hand is ten or less, counting Ace 1,numerals face value, courts 10 each. A 'gin' hand is one in which all ten cards are melded, and scores extra. Keep playing till either player knocks, or there is only two cards remain in stock. In the latter case the game is a no-score draw and the deal passes. You knock (by knocking of course) by making a final discard face down to the waste pile and spreading your other ten cards face up, separated into melds and deadwood. Your opponent then makes whatever melds he can, lays off any cards that match the knocker's melds-unless you went out 'gin', when this not permitted- and reveals his deadwood. The knocker normally scores the difference between the values of both players's deadwood, plus a bonus of 20 if he went gin. However, if he didn't go gin and if his deadwood is equals or exceeds that of his opponent, then the latter scores the difference between the two, plus a bonus of 20 for the 'undercut'.
Game.
The deal alternates and scores are kept cumulatively. The winner is the first to reach or exceed a total of 100. The winner score the difference between the two scores (double it if the loser fail to win a hand) plus 100 for the game plus 20 points for each hand (box) he win more than the loser. (for example the winner won 7 hands, the loser won 3 hands therefore the winner received 80 points), except when the number of the winner's hands is least than the loser's hands, the winner received a minus score instead.
sample of a score:
OK let say 'we' won the first hand and got 34, second hand 'they' won and got 12, on the third hand 'they won again and got 19 making thier current total of 31. But 'we' won the next three hands winning with a score of 105. The 'we' player received 74 from the different (105-31=74). 100 for winning the game. 40 points for winning two more hands than 'they' (2x 20=40) and so giving the grand total of 214. This can be played with a small stake.
Gin Rummy variants.
There is not much variants for this game except for the scoring. The bonus (undercut, gin and hands)can be 25 instead of 20 and the game 150 instead of 100. There also a special scoring called The Hollywood method.
For three players (known as Jeresy Gin) It played the same way as the two hand Gin.
1) The winner score the difference bteween his own hand and that of each opponent.
2) There is no bonus for undercut; instead, the knocker subtract 20 (or 25 by agreement) from his score.
3) Opponents may lay off cards only against the knocker's original melds- not against each others and not against a card already laid off by the other.
4) The bonus for gin is 50.
5) If no one melded when only three cards remain in the stock, the game is a no score draw.
6) Game is 200 up.
Even more pointless are forms of partnership Gin for any even number of players whereby all is play two handed but scores are lumped together in teams.
For the Hollywood scoring see here.
Sources:
Websites: pagat.com and Rummy-Games.com
Books: The Penguin Book of Card Games (2008) by David Parlett
The Complete Book of Card Games (2001) by Peter Arnold
Teach Yourself Books: Card Games for Two (1969) by Kenneth Konstam
