
a game for 23 players
The game is played on a five by five grid. On your turn, you place a card in an open spot, score points depending on the connections between the played card and nearby cards, and possibly draw cards depending on those connections. You are penalized for any cards left in your hand at the end of the game.

Setup
Shuffle the basic deck.
With two players, deal 12 cards to each player; with three players, deal 8 cards each. Then turn one card faceup in the middle of the table. The remainder of the deck forms a draw pile.
Play begins with the player on the dealer's left and continues clockwise.

Game play
On your turn, select one card from your hand and place it into an open space next to a card already in play. You must place the card so that its edge is next to another card; diagonally adjacent is not enough.
Your play may score points in several different ways: Basic scoring, pairs, sequences, and power plays. See below. If the total is negative, then you lose points for the turn.
Over the course of the game, cards will be added to complete a 5x5 grid. So when the cards in play fill an area five cards wide, further plays cannot be outside those bounds. Until the spread of cards has grown to five cards in a direction, cards may be added to either end. The initial card might be in the middle, on the edge, or even in a corner of the final board.

Scoring
Basic scoring: Consider this card (the one you played) with respect to each horizontally or vertically adjacent card. Diagonals don't count for basic scoring. Add the rank of the two cards together.
 If the sum is 9 or less: Lose points equal to the sum of the two cards. The Ace Matching exception: If one of the cards is an Ace and the two cards share a suit, then gain those points instead of losing them.
 If the sum is exactly 11 or 20: Draw a card.
 If the sum is between 12 and 19: Add points equal to ten less than the sum. For example, a 6 next to a 7 (total 13) makes for 3 points.
Pair: If this card is the same rank as an adjacent card, add 5 points.
Straight: If this card completes a continuous line of three or more cards that are in rank order, add 20 points. Straights may be horizontal, vertical, or diagonal. If you make more than one straight, score for each.
Three of a kind: If this card completes a continuous line of three or more cards of the same rank, add 30 points. Threes of a kind may be horizontal, vertical, or diagonal. If you make more than one three of a kind, score for each. Cards that contribute to three of a kind may not be scored as pairs.
You may score several bonuses, but they must be in different lines. For example, playing in the middle of a four card straight doesn't count as two overlapping three card straights. Playing so that your card completes two straights in two different directions does score twice (for 40 points).
Power play: If this card is an Ace or Crown and you play it adjacent to an Ace or Crown of the same suit, then you score a power play. Add the total value of all other cards of that suit which are in play. This may be as little as zero (if there are no other cards of that suit in the grid) or as many as 44 (if all the other cards of that suit are present in the grid.)
Since the Ace and Crown sum to 11, you will draw a card as part of basic scoring when you make a power play.

The end of the round
The round ends when all 25 spots are filled. If you drew cards as the result of play during the round, then you will have at least one card left over at the end. You lose points for each card left in your hand: Subtract the rank of each number card, subtract 10 for each Crown, and subtract 15 for each Ace.

Solitaire
As a solitaire, Quincunx is played against the tableaux in an attempt to earn as many points as possible.
The solitaire game is played on a 4x4 grid. Starting cards are dealt in each of the four corners. Deal yourself an 8 card hand. Scoring is as per the usual rules, except that Straights and Threes of Kind may not be scored on diagonals.
If you run out of cards before completing the spread, you lose. This means that you will need to arrange basic scoring for 11 or 20 several times. Don't do it too many times, though, because cards in your hand at the end still count as a penalty.
Credits
Quincunx is a game by Chris DeLeo.
The solitaire variant was suggested by Jack Neal, and the singlecard starting configuration was suggested by Nate Straight.