Solitaire

Klondike solitaire — build the four foundations up by suit. Tap to move cards, flip the stock and chase your best time.

Klondike shipped with Windows 3.0 in 1990, and Microsoft has said the goal was teaching mouse skills — dragging in particular — to people who had only used a keyboard. It became one of the most used pieces of software ever written.

The honest statistic is that it is not always winnable. Depending on rules and whether you can see the stock, somewhere between about 79 and 92 percent of deals are theoretically solvable, and human win rates sit far below that. This is called the problem of Klondike solitaire in the literature precisely because the exact figure resisted calculation for a long time.