A card game for two players and one deck of cards.
Players sit on opposite sides of a playing area (it's most comfortable to play at a table). Both players must be able to reach to a point midway between them without difficulty. Players take turns each game being dealer. The dealer shuffles the deck thoroughly and deals 15 cards face-down to each player. The deck is placed face-down midway between the players. Both players arrange their 15 cards as follows:
+----+ +----+ +----+ +----+ +----+
| | |down| |down| |down| |down|
| up | +----+ +----+ +----+ +----+
| | | | |down| |down| |down|
+----+ | up | +----+ +----+ +----+
| | | | |down| |down|
+----+ | up | +----+ +----+
| | | | |down|
+----+ | up | +----+
| | | |
+----+ | up |
| |
+----+
where the cards are face-up or face-down as shown.
Each player must sit on one hand. Normally this is the non-dominant hand, but if a more experienced player is playing against a novice, a handicap may be awarded so the more experienced player must sit on his/her dominant hand. The dealer makes the first draw, and players alternate draws until one player has no cards left - that player is the winner.
A player draws by taking the top card from the deck and placing it face-up next to the deck, on the 'pile'. (The player drawing is not allowed to look at the card before putting it on the pile, it should be moved as quickly as possible.) A player may place a face-up card from the 'triangle' in front of them onto the pile if the rank of that card is one different from the rank of the card at the top of the pile (e.g., 5 can go on 4, Jack can go on Queen). (There is wraparound from the King to the Ace.) If two people try to play at once, the player who gets the card down first has the valid play, the other player must return the card to the triangle. For example, if a 7 is on top of the pile and one player plays a 6 and the other plays an 8, the card which ends up on top is of course not one rank different than the one below and must be retracted. The speediest player has the advantage. If one of the five columns of the triangle is empty, any face-up card from the triangle may be moved to that column. Once a player has played (or moved) a face-up card, if a face-down card is exposed the player has the option of turning it face-up. The player is not compelled to do so, one is allowed to play (or move) another card even when there are exposed face-down cards in front of one, but of course it's a good idea to do it as quickly as possible to maximise the chances of playing cards quickly. When both players agree that they no longer wish to play on that draw, another draw is made. If the deck runs out, the pile is shuffled and placed face-down to serve as the deck again. (At this stage only is it permitted to use both hands in the middle of the game. Unless, of course, you just have to show off how you can shuffle a deck with just one hand.)
It is a fast game. But there is also some strategy. For example, if an Ace is on the top of pile, and you have only an Ace and a 2 left and your opponent has only a 3… you have the option of trying to play the 2 and then the Ace, but your opponent will most likely be able to slap down the 3 before you have time to reach back for the second card. In this case, it is better not to play, and hope that the next card drawn is a King. If you get a King, you can play the Ace then the 2 and win before your opponent gets to play the 3. (Or, you can hope it's a 2 and hope you're faster with the Ace than your opponent is with the 3. If you draw a 4 you'll lose for sure, but you've a better chance of winning by drawing than by playing.)
Ah, I see that yerricde has already noded speed card game. There's a variation on the rules over at that node.