Solitaire

Solitaire (also known as Klondike) is a card game that was bundled with Microsoft Windows from Windows 3.0 through Windows 7. The goal of the game is to arrange all of the cards in each suit in a complete sequence from Ace to King. The player wins if the player successfully manages to place all of the cards into their respective suits. Since Windows 8, an updated version of the game was introduced as part of the Microsoft Solitaire Collection.

Its inclusion in Windows 3.0 was intended to introduce computer users to graphical user interfaces and to familiarize them with using the mouse such as the drag and drop technique. It eventually became an iconic part of the operating system with The Strong National Museum of Play inducting it to its World Video Game Hall of Fame in 2019. As of 2020, over 35 million active monthly players have played Microsoft Solitaire with more than 100 million games played daily.

Debug version
The checked/debug builds of Windows NT 4.0 (and early checked Windows 2000 builds) includes a debug version of Solitaire in place of the standard version. This version is unique from the retail version in that it sets decks up by a game number instead of randomly (akin to FreeCell) and includes a hidden menu between the Game and Help tabs for accessing select debug features. These debug features includes manually changing the game number, printing numbers to represent the size of each deck, automatically win the game, or cause an assertion error that doesn't crash the application.

The free/retail versions of Solitaire lacks the debug menu, but the game number and assertion error dialogs still exist within the code for the version used up until Windows Vista build 5048.