UNO Online is an online turn-based discard card game that's similar to the offline UNO card game. The player receives an initial hand of seven cards. They must discard or shed all of these cards and any additional cards that they pick up during play to win against one, two or three virtual opponents.
When it's the player's turn, they discard a card based on the color, number or symbol on a face-up card to the left of a deck. If their hand lacks the right kind of card, they draw a single card from the deck. If the card matches the face-up card, they must discard it. If they don't have a match, their opponent takes their turn. If they have only one card remaining, they must immediately select a button shaped like a diamond made of four different colored diamonds and marked with a "1" or receive a penalty of two extra cards from the deck.
During gameplay, 4 Colors PGS gives the player four specialty cards (Action, Reverse, Skip, Wild and Wild 4) to make winning more difficult. With Action (a hand with two cards), the player forces their opponent to draw two extra cards and give up a turn. With Reverse (double curved arrows), they switch around the order of the turn-based play. With Skip (a prohibition circle), they bypass the other player's turn to discard twice in a row. With Wild (a black card with a diamond made of four colored diamonds and diamonds at each corner), they change the color for the next turn. Lastly, with Wild 4 (a black card with a hand holding four cards), they choose the next color and force their opponent to draw four extra cards.