Kemps is a fairly simple to grasp, extremely difficult to master card game. I've also heard it called Kims and James.

52 cards
3 friends (No, that doesn't include you.)

Conspire with your partner in a corner somewhere. You need to come up with a signal. You will want a subtle gesture - maybe even a vocal clue - anything, be creative. Use of the signal will be discussed shortly. Shuffle the cards. Position yourselves on 4 sides of the table, partners across from each other.

Collect 4-of-a-kind and signal this to your partner, at which point he will call out "Kemps", winning the round. Complete this discretely enough that the opposing team does not call "Anti-Kemps" (or "Anti"), catching you with four-of-a-kind and winning the round for themselves.

Look at the four cards in your hand that were dealt to you. Dealer puts four cards into the pit, face up, one at a time. Once the fourth card is down, its a free-for-all. Switch cards into and out of your hand. Once all is still and everyone has four cards in his hand, confirm that everyone is done with the cards left in the pit and turn them over into a discard pile. "Kemps" and "Anti" may be called at any time during the game by any player. Continue dealing four cards at a time in as many mini-rounds as it takes for someone to win the round.

"Kemps" may only be called when the teammate with four-of-a-kind has no extra cards in his hand. Conversely, "Anti" may be called with any number of cards in the opposing team members' hands, and wins the game if a four-of-a-kind is present.
One incorrect "Anti" is allowed per team per round, the second false call will lose the round for the calling team. One incorrect "Kemps" automatically loses the round for the calling team.
If you run out of cards, reshuffle the discard pile and start over.

Designate who you and your teammate will watch. As you are switching your own cards in and out, keep track of what the opponent that you are watching is picking up.
Analyze the situation. If your watchee is switching one card in and out every round - for example exchanging a 2 for a 4, then a 4 for a 6, then a 6 for a 7, think about it. He's holding onto the same 3 cards looking for that last card. If you're a good watcher, you'll know what those 3 cards are anyways. When he picks up the 4th, call "Anti".
Pick subtle but easly recognizeable signs. Also the duration of the sign should not be too short. A different way of holding your cards is better than a quick hand gesture - scrathing your face, for example. What if your partner doesn't see the sign right away? It's a bit less obvious to sit still and be executing the sign than scratching your face off.
Look for the sign. The best offense is a quick call after getting four-of-a-kind. The best defense is watching like a hawk.
Be patient with the game. It gets really interesting as the players get better.

That's about it. If you have any questions or anything to add if you've played this before, let me know - I'm interested to know who has heard of this and who will try it out.