This is a simple game of solitaire using an ordinary deck of SET® cards. This game is completely strategy-less, but is a good way to pass a little mindless time in places like airport terminals, car passenger seats, etc. You don't win too often, but you can pretty easily get close enough to keep yourself interested...
One deck of SET® cards.
Hold the deck in one hand, face down. Pull cards from the bottom and place them face up on top, one at a time. After each card is pulled (and there are at least three cards turned up), compare it with the next two cards down the stack, and try to remove some cards according to the following rules:
Whenever cards are discarded, repeat the comparisons/removals using the 3 cards that are now the top 3 cards. (Reasonably astute observers will realize that this is useful only in the first case, where only one card was removed.)
The goal is to end up with 0 cards after passing through the entire deck once.