UNO has a new best friend, DOS. In this fun card game, two is more important than one, and number matching is king. Just like UNO, DOS involves a race to be the first to get rid of your cards. To start, there are two discard piles between the players. On each player's turn they can discard on either pile with either one or two cards, so if a player has two cards that add up to the number of a card in the center pile, they are able to put down both cards.