There is no definitive answer to this question, of course. It's mostly a matter of opinion. That being said, the following games certainly belong in the discussion of the most popular solitaire games of all time:
- Klondike - Due to its being included in every version of Microsoft Windows (where it's known as Windows Solitaire), Klondike has been played by millions of people, and is probably the best-known solitaire game in the world. Many people don't even realize that other games exist.
- FreeCell - Thanks (again) to Microsoft, which included a version of the game in Windows 95, FreeCell has become one of the world's most popular solitaires. Unlike Klondike, the vast majority of FreeCell hands can be won, given sufficient patience and foresight.
- Spider - The third of the Microsoft-boosted solitaire games, Spider is perhaps the best-known two-deck solitaire game.
- Cruel is another game with a Microsoft connection, having been published in "Windows Entertainment Pack #1" way back when.
- TriPeaks was popularized by its ubiquitous presence in bar-top arcade machines, where its simple rules, fast gameplay, and limited strategy made it a favorite.
- Canfield (also known as "Demon") is a simple-to-play but difficult-to-win solitaire that was popularized in the late 1800's as a saloon gambling game.