Hofer's The Games We Played includes pictures of cards from The Improved Game of Snap, made by the McLoughlin Brothers of New York in 1889 (p. 32). There still are commercially-made Snap cards, but the game can also be played with a standard deck of playing cards. The game is noisy, but it's a fun classic card game for kids (The Diagram Group 304). Actually, it might be the ideal kids' card game because it doesn't matter if the deck is slightly damaged or even missing a couple of cards.
The rules for this game come from The Way to Play by the Diagram Group, p. 304.
Players: 2 or more
Object: To win all of the other players' cards.
The Deck: You can use a commercially-made set of cards specifically designed for the game, or you can use a regular 52-card deck. (It's best to use a deck that you wouldn't mind getting damaged. It's a fast-paced game, and it can be a bit rough on the deck. It doesn't even matter if there are cards missing from the deck. A couple of missing cards aren't likely to be noticed, and it won't make any difference in play.) For groups of 4 or more, it helps to use two decks instead of one.
Deal out all of the cards in the deck clockwise around the table, face down. Depending on the number of people playing, the players may not all have the same number of cards in their hands, but that's okay. The players do not look at their own cards; they keep them in a pile, face down in front of them.
Each player, starting with the player sitting to the left of the dealer, turns over the first card on his pile. Players continue turning over cards and putting them face-up on top of the ones they've already turned over, moving clockwise around the table, until someones spots two cards with matching values face up on two different piles. When someone sees two matching cards, he yells "Snap!"
Of course, other players will spot the matching pair and yell "Snap!" too. Players have to pay attention and speak up as quickly as possible. The first person to yell "Snap!" gets to keep both of the face-up piles with the matching cards on top and put them on the bottom of the face-down pile of cards in front of him.
After the piles of cards have been given to a player, players continue laying down cards just as they did before, picking up where they left off with the player who was next when someone yelled "Snap!" Everyone continues laying cards face-up on their piles until the next time there's a pair and some yells "Snap!"
The Pool: With several people yelling at once, it can be difficult to tell who was first. If two or more people seem to yell at the same time, the piles that would have been given to the first to yell are put in the middle of the table. The pile of cards in the middle of the table is called the "pool." A player can win the pool by yelling "Snap pool!" when he spots a card matching the one on top of the pool face-up on a player's card pile. The first to yell is the one who wins the pool.
Penalties: If someone yells "Snap!" at the wrong time (when there are no matching cards face-up), there are a couple possible penalties:
The choice of penalty is up to you, but decide ahead of time, so everyone knows what to expect.
Running Out of Cards: When someone runs out of cards in his face down pile, he can turn any face-up cards he has in front of him over and use them again. If someone is completely out of cards, face up or face down, that person is out of the game.
Winning: The winner is the one who wins all the cards in the end, leaving the other players without any.
Speed Variation: To make the game faster, players can turn over their next cards all at the same time instead of taking turns around the table.