Klondike Solitaire — move all cards to the foundations!
Klondike Solitaire is the world's most-played card game. It became famous as a pre-installed game on every Microsoft Windows computer from Windows 3.0 (1990) through Windows 7, where it was used to teach users how to use a mouse — drag-and-drop on cards was the perfect way to learn the new interaction model. By the time Windows 8 removed it from the default install, billions of people had played it.
The game dates back to 19th-century North America. "Klondike" refers to the Klondike Gold Rush region of Canada's Yukon territory — the same era card game variants spread across prospector camps. The objective is to build four "foundation" piles, one per suit, from Ace to King. Cards in the main tableau (the seven columns) are organized in descending order and alternating colors to make them movable and useful.
Interestingly, not every Klondike deal is winnable — statisticians estimate that about 79% of games are theoretically solvable, but players only solve roughly 43% in practice because the optimal sequence of moves is not obvious.