The aim of this game, which is played with a standard international pack, is to collect a hand of five cards of the same suit, which then scores the total value of the cards counting pictures as 10 and aces as 11. Different versions of it are played in China and Japan. The Chinese game, known as wŭshíyī fēn (五十一分) or wŭshíyī diăn (五十一点) (fifty-one points) is apparently played only in the northern part of Fujian province, around Nanping city. The Japanese version, which is simpler but clearly related, is well-known in Japan, but thought of mainly as a children's game.
This description is based on information from Zhang Chuansheng, Linda Wang and Mae Channing.
A standard international 52-card pack is used. Numeral cards 2-10 have their face values, jacks, queens and kings are worth 10 points and aces are worth 11.
This game is normally played by four players, or sometimes by three. In principle it could be played by two or five players, but it is best for three or four.
Deal and play are anticlockwise.
The cards are dealt in the Chinese manner. The cards are shuffled and stacked face down. Then the starting player draws the top card of the pack, the next player to the right takes the next card, and so on, taking cards one at a time in turn until the starting player has a hand of six cards and each of the other players has five cards.
I do not know what procedure is normally used to decide which player will start. I suggest choosing the starting player for the first deal at random by drawing cards, and that the turn to start should pass to the right after each hand.
The starter begins the play by discarding any one of his six cards face up on the table, next to the stock. From then on, the turn to play passes anticlockwise and at your turn you have the following options:
a) If all your cards are of the same suit you may 'call'. The play ends immediately and the hands are scored.
b) You may draw a card from the top of the stock, add it to your hand, and then discard any one of your six cards face up to the table, alongside any face up cards that are already there. If there were already five cards face up on the table, these five cards are set aside face down and the new discard remains as the only face up card.
c) Instead of drawing a new card, you may exchange all the face up cards on the table for an equal number of cards from your hand. You first discard the appropriate number of cards from your hand, and then pick up the cards that were face up on the table, leaving your discards as the new set of face up table cards.
d) If there are exactly five cards face up on the table, you may exchange one card from your hand for any one of the face up cards on the table.
In case (b), (c) or (d), if at the end your hand has the maximum value 51, consisting of the A, K, Q, J, 10 of one suit, you can declare it immediately and end the play.
Please note that:
When a player declares 51 or calls or the stock is exhausted, play ceases and the hand is scored.
In order to score points, a hand must consist of five cards of the same suit. Then the value of the hand is the sum of the value of the cards. The maximum value is 51, for a hand consisting of A-K-Q-J-10 of a suit.
Declaring 51 points is known as míng suàn (明算 - a clear count). The caller scores double - 102 points - and any other players who have five cards of the same suit score the values of their hands.
Calling with less than 51 points is àn suàn (暗算 - an unclear count). In this case the caller places his cards face down on the table. The other players in turn have the opportunity to challenge the caller: challenging is known as dĭng (顶). The hands are then compared. If the caller's hand is higher than the challenger's hand, the caller scores the sum of both hands while the challenger scores zero. If the challenger's hand is equal to or better than the caller's, the challenger scores for both hands and the caller scores zero. In either case, players who did not challenge just score the values of their hands. Example: A calls, B passes, C challenges, D passes. A has a hand worth 48, B has 45, C has 48, D has 49. The scores are A: 0, B: 45, C: 96, D: 49.
If more than one player challenges the caller, the winner scores scores the value of the caller's hand plus the values of all the challengers' hands while the other players involved in the challenge score zero. I am not certain what happens in case of a tie for best hand between two or more challengers. I suggest that the last challenger involved in the tie should win. Example: A calls, B passes, C challenges, D also challenges. A has a hand worth 49, B has 47, C has 50, D has 50. The scores are A: 0, B: 47, C: 0, D: 149. If any player can clarify this rule for me, please let us know.
A cumulative score is kept for each player and the game continues until some player has a total score of 500 or more. At that point the player who has the highest total score wins. I do not know what happens in case of a tie at 500 points or more. Perhaps further deals are played until there is a clear winner.
Jokers. Often two jokers are included in the deck. These act as wild cards, belonging to whatever suit the holder needs, and have a value of 10 points. Some play that if two hands are otherwise of equal value, a hand without a joker is better than a hand including a joker.
Some play that you can only call if your hand scores at least 42 points.
Naturally the target score for ending the game can be changed to make the game longer or shorter. For example some play until a player has 1000 or more points.
Some play that a hand containing four cards of the same rank is a bomb. It does not matter what the fifth card is - for example 8-8-8-8-5 is a bomb. A bomb qualifies as a clear count (míng suàn: 明算). A player who has a bomb can declare it immediately and scores 204 points, while all other players score the values of their hands.
This description is based on information from Kuromiya Kimihiko.
51 is a popular family game in Japan - its Japanese name is goju ichi. As in Chinese 51 the aim is to collect cards of the same suit in a five-card hand, the maximum score being 51, but the scoring and the play mechanics are different and more straightforward.
A standard 52 card deck is used, sometimes with one joker added. Aces are worth 11 points, king, queen and jack are worth 10 and numeral cards 10-2 have their face values.
The game is best for four players, though in principle it could be played by from 2 to 5 people or maybe even more. Deal and play are clockwise.
The dealer deals each player five cards, one at a time, and then turns the next five cards face up and lays them on the table. The remaining cards are placed face down to form the stock.
The player to dealer's left begins, and the turn to play passes to the left, clockwise around the table. (Variant: some play that the dealer begins.)
In each turn a player must pick up one of the five cards on the table, add it to his hand, and then discard a different card to the table.
After everyone has had one turn, a new option becomes available. Any player who does not want any of the cards on the table may begin his turn by clearing the table. He puts the five cards aside and turns up the top five cards on the stock. The table can only be cleared once in a turn, so having cleared the table the player must pick up one of the five new cards even if he wants none of them. If there are not enough cards in the stock when a player wishes to clear the table, the cards previously put aside are shuffled to form a new stock.
Players are not allowed to clear the table at their first turn to play.
At the end of his turn, after picking up and discarding, a player may say 'Stop!' if he thinks he has a better hand than any other player. After this each of other players has one more turn, and then the play ends.
The value of a five card hand is calculated by adding up the value of the cards held in any one suit, and subtracting from it the value of the cards held in the other suits. For example, if you have the Ace of hearts, the Queen of hearts, the 9 of hearts, the 3 of spades and the 2 of diamonds, you have 11 + 10 + 9 - 3 - 2 = 25 points in your hand. It is possible to have a negative number of points - for example with Queen of clubs, 7 of clubs, 9 of diamonds, 5 of diamonds, 10 of hearts your score is 10 + 7 - 9 - 5 - 10 = -7.
The player with the highest hand value is the winner. If there is a tie involving the stopper, the other player wins the game. If there is a tie between two or more players other than the stopper, then all players involved in the tie win.
When a joker is added to the pack, it can be used to stand for any card not in the player's hand. That means that in practice it is worth 11 points if the holder does not have the ace of the suit, or 10 points if the ace is present. So this hand: 
A-9-
K-Q-Joker is worth 11 points (31-20) using the joker as a heart, but almost any exchange will improve it.
Some play that after a player has called 'Stop!' the table cannot be cleared. Instead each of the other players in turn has the option to exchange one card for one of the cards on the table or to pass, doing nothing.
Some play that a hand only scores if all the cards are in one suit. A hand containing two or more suits scores zero.