FreeCell is a solitaire card game similar to Klondike.

Rules

A game of FreeCell running on Ubuntu Linux (GNOME).Shuffle, then deal the 52 cards face up in 8 columns with each card visible but only the end card of each column fully exposed. Four columns will have 7 cards, the others only 6. 
Apart from the columns, there are four single card free cells and four suit piles (foundations). The objective is to get all the cards into the foundations. 
Single exposed cards may be moved: 
Column to column, placing the card on a card of the next rank and different colour suit. (E.G. Place a red 3 on a black 4.) (Aces are low.) Or placing the card on an empty column. 
Column to FreeCell, any exposed card as long as there is an empty cell. 
FreeCell to Column, as column to column. 
Column to suit home pile. Next card in order, starting with the Ace, ending with the King. Each suit is completely independent. 
FreeCell to suit home pile. As column to suit home pile. 
The terms in italics are defined in solitaire terminology.


History
One of the oldest ancestors of FreeCell is Eight Off. In the June 1968 edition of Scientific American Martin Gardner described in his "Mathematical Games" column, a game by C. L. Baker that is similar to FreeCell, except that cards on the tableau are built by suit instead of by alternate colors. This variant is now called Baker's Game.

Paul Alfille changed Baker's Game by making cards build according to alternate colors, thus creating FreeCell. He implemented the first computerized version of it for the PLATO educational computer system in 1978. The game became popular mainly due to Jim Horne, who learned the game from the PLATO system and implemented the game as a full graphical version for Windows. It was first included with Microsoft Win32s as a test program, but was made a part of Windows 95 and has been included with every version of Windows since.

Today, there are many other FreeCell implementations for every modern system, some of them as part of Solitaire suites. However, it is estimated that as of 2003, the Microsoft version remains the most popular, despite the fact that it is very limited in player assistance features, such as retraction of moves.


Strategies
A sequence of several cards with alternating colors can be moved at once by moving cards to vacant cells and/or temporarily placing them in empty columns. If the move involves temporarily placing a card in an empty column it is called a supermove in FreeCell terminology.

Cards can be safely moved to the foundations without a chance of being further used, if the value of the foundations of the different color are greater than the card face value minus 2, and the value of the other foundation of the same color is greater than the card face value minus 3.


Difficulty
Like Minesweeper, FreeCell is a provably hard (NP-complete) game. This result was proved in 2000 and first published in 2001.[1] The result implies that writing a computer algorithm that finds solutions for arbitrary FreeCell configurations quickly would be a major scientific breakthrough. A perfect FreeCell playing program would earn the discoverer a $1,000,000 prize for solving one of the Clay Mathematics Institute's Millennium Prize problems. However, most researchers believe that no such solution procedure exists.


Culture
FreeCell, highly popular in the United States, has developed its own subculture.


Versions
While there are actually 52!, or approximately 8.06x1067, possible games, some games may be similar to others due to the fact that suits assigned to cards are arbitrary. When a card is black, for example, it may be assigned to clubs or spades.

The original Microsoft package includes 32,000, generated by a 15-bit random number seed. These games are known as the "Microsoft 32,000". Later versions of Microsoft FreeCell include more games, of which the original 32,000 are a subset.

The original Help file remains through modern Microsoft versions: "It is believed (although not proven) that every game is winnable." This was known at the time to be untrue in its strictest sense. Games numbered -1 and -2 were included as a kind of easter egg to demonstrate that there were some possible card combinations that clearly could not be won. Nevertheless it started a flurry of interest in the question of whether all of the Microsoft 32,000 could be beat. Smart players could win most games most of the time, but that wasn’t proof either way.

The Internet FreeCell Project by Dave Ring, which was finished in October 1995, took on the problem. Ring assigned 100 consecutive games chunks across volunteering human solvers and collected the games that they reported to be unsolvable, and assigned them to other people. This elegant project used the power of multiprocessing, where the processors were human brains, to quickly converge on the answer. Only one game defied every human player's attempt, the famous game number 11,982.

In later implementations of Freecell in Microsoft Windows, there are 1,000,000 games. Of these 1,000,000 games, 8 have been found to be unsolvable. They are games No. 11,982, No. 146,692, No. 186,216, No. 455,889, No. 495,505, No. 512,118, No. 517,776, and No. 781,948.

One way to "win" at any Microsoft Freecell game was added as a way to help the original software testers; push Ctrl-Shift-F10 at any time during the game. Click Abort to win, Retry to lose, or Ignore to cancel. Double-click any card for the results. Unfortunately this doesn't actually solve the game, it just throws the cards into electronic piles without regard for the rules.