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Basic rules
The game is played by 2-4 players.
Each player gets 7 cards at the start of the game.
The objective is to get rid of all your cards by putting them onto the pile.
You can put down a card if it has the same suit or rank as the top card of the discard pile. E.g. if the card of the pile is a 5 of spades then you can play any spade or any 5.
If you have no cards you can play then you must drag one card from the stock and don't get to do anything else during that turn.
If you have two or more cards of the same rank then you can play them together. E.g if the card on top of the pile is a diamond and you have a four of diamonds and a four of spades then you can play them together, thereby changing the suit of the pile to spades. To do that you right click on all the cards in the order you want to play them, and then left click on one of them to actually put them on the pile. If you are playing on an iPad or another tablet you can click a card and hold the finger on it for a second, then it will be selected. Select the ones you want to play together, and then tap on one of them to play them all together.
Power cards
To make the game more interesting there are a number of cards that are special:

Twos2: If a player plays a two, then the next player must draw two cards and cannot play any cards, UNLESS he has a two as well in which case he can play it and the next player him must draw 4 cards. This can go on as long as players have two's, and increases by two each time, e.g. if three players have played two's in a row then the fourth player must pick up six cards.

Sevens7: Dump the suit. All other cards in the same suit as the 7 may be played in the same turn. Do this by first playing the 7, then all the other cards of the suit will rise slightly in your hand and you will be prompted to play them. Click on them in the order you want to put them out. Any special cards put out after a 7 play will not have their normal effect, e.g. if you play a 7 of spades and then dump a 2 of spades it will not cause the next player to draw extra cards. You are not forced to get rid of all the cards of the suit, if you have a card of the suit you want to keep you can right-click on it and it will not be played.

Eights8: When an 8 is played the next player misses his turn. Playing two or more eights together does not have any extra effect.

Tens10: Reverses the direction of the game. E.g. if the game was going clockwise then it will start to go counter-clockwise and will continue like that until another 10 is played.

Black JacksBlack Jack: When a player plays a Black Jack the next player must draw 5 cards. Two Black Jacks can be played together, in which case the next player must draw 10 cards. If player 1 plays a black jack, then player 2 may also play a black jack if he has it and then player 3 will have to draw 10 cards.

Red JacksRed Jack: The Red Jack cancels out a Black Jack. If player 1 plays a Black Jack then player 2 can play a Red Jack and then he won't have to draw 5 cards. If player 1 played 2 Black Jacks then player 2 can either play one Red Jack and draw 5 cards, or play two Red Jacks and draw no cards. The Red Jack is only effective against a Black Jack, you can also play it like any other card but it won't have any special effect.

AcesAce: Ace can be played no matter what suit is on the table, and when a player plays an Ace he gets to decide what suit the table changes to. This is essentially the same as an 8 in Crazy Eights.

Black QueensBlack Queen: Player changes hands with the player left to him. E.g. if player 1 plays Black Queen, then player 2 will get all of player 1's cards, and player 1 will get all of player 2's cards. It's a good card to play if the player left to you has fewer cards than you do.