1 Deck. Easy (94%). Mostly Luck.
Object
To discard all the cards in pairs.
Layout
•  25 Piles arranged in a 5x5 square  discard pairs of cards that add to 15 that are adjacent to each other, either horizontally, vertically, or diagonally (to discard a pair, drop one of the cards on the other, or rightclick on one of the cards). Discard Aces singly, by clicking on them. 
Notes
•  Pairs of cards that add to 15 are King2, Queen3, Jack4, Ten5, 96, 87. 
•  Whenever a pair (or Ace) is discarded, the remaining cards will be moved to the top in the following way: spaces are filled by moving cards to the left. If there are spaces on a higher row, a card is moved from the leftmost pile of the lower row to the rightmost pile of the higher row. New cards are dealt to fill the spaces at the bottom. All the cards are moved in this way until all the spaces are at the bottom. 
History
Monaco is a variation of Monte Carlo. It was invented by Thomas Warfield. It has the same layout as Monte Carlo, but cards are discarded in pairs that add to 15 rather than pairs of the same rank. Also, spaces in the layout are filled immediately, rather than only when the fill button is presses, making for a more dynamic game.
Similar Games
Monte Carlo
Fourteens
