Quad-Ominos is a game published by Pressman beginning in 1978. It is permanently out of production but generally available on the secondhand market. It is similar in theory to Triominoes but uses a set of four-sided square tiles. The object of the game, as with many domino-type games, is to rid one's hand of tiles by placing them all on the board.
Each tile is made of a stamp-molded polystyrene plastic, colored white or cream, and is approximately 1" square with rounded corners, and approximately 1/4" deep. Each tile has four numbers, one on each corner, painted in brown or black. The numbers normally have a raised relief; the tile's numbers can, with skill, be discerned by touch. The backs of the tiles are hollowed out, unlike most other tilesets like dominoes and triominoes.
The numbers range from 0 to 5, and each tile contains a unique combination of four numbers (with replacement). There are 125 tiles in the set; the number of possible combinations of 6 values taken 4 at a time with repetition is 
, but the tile with combination "0245" is absent from the set.
The numbers on each tile are placed in one of several arrangements; the most common is a clockwise or counter-clockwise arrangement in ascending order. The tile with the unique combination "0224" might look like:
The game begins with all tiles turned face-down (alternately they can be placed in a bag); they are then shuffled (or the bag shaken) and each player picks a number of tiles:
Each player's tiles are laid on-edge facing towards the player.
Play begins with the highest "quad" (tile where all four corner values are the same); if no such tile was drawn, play begins with the highest-value tile drawn (the tile with the highest total of corner values). That tile is laid down in the center of the table, the player scores the sum of the corner indices, and if this tile was a quad, the player gets their choice of a 25-point bonus or the opportunity to play 2 additional tiles, scoring their values as well. If the player with the starting tile also has the "quad-zero" tile (with zeroes in all four corners), he may choose to play that, and take both the 25-point bonus and the opportunity to play 2 additional tiles.
In turn, players then lay one tile each per turn with at least one side of the tile contacting the side of another tile already played, and score points equal to the sum of the corner indices on that tile. A tile can only be played to a position on the board if the numbers at its corners match those of adjacent tiles. Adjacent tiles are tiles immediately contacting any of the played tile's 4 sides, and any tiles in the four diagonal directions (even if there is no tile contacting either side forming that corner). A tile must be laid orthoganally to at least one other tile (directly adjacent with one side completely contacting the side of the other tile); a tile cannot only be diagonally adjacent to other tiles. A valid play must match at least two numbers, but may match three or all four.
If a tile is placed such that more than two of its numbers match tiles on the board, the player placing the tile gets the option of adding a 25-point bonus to their score, or playing two additional tiles. If the player chooses to place bonus tiles, a bonus tile can be placed such that it would also match more than two numbers. The instructions for the Pressman game do not specify if a bonus tile can trigger an additional bonus; they do specify that if a player cannot play two additional tiles, their only option is to take the bonus.
If a player cannot make any play on their turn with the tiles in their hand, they must draw tiles one at a time from the boneyard (called the "well" in the instructions). For each tile drawn this way, the player incurs a 20-point penalty. If a player cannot play and the well is empty, they take a single 20-point penalty and must pass.
A player wins a single round by being first to play all tiles in his hand to the board. All other players then count up the total value of the remaining tiles in their hand, those totals are summed and the winner receives those additional points. The first player to reach an overall score of 800 points wins the game. The threshold could be any number of points; 800 is from Pressman's rules.