"I played a game of Solitaire with a deck of tarot cards once. I won, but five people died."
--old joke
The Klondike and Freecell rules are possibly the most popular things one can play with a deck of playing cards. So ingrained in card playing culture they are, that any time there is a new and different kind of deck to play with, they are the template by which new rules tend to be devised. I, personally, have seen variations played with Mahjongg cards, and it's not terribly difficult to make them work on German or Spanish cards either. But say you have a deck of tarot. In addition to the four suits with their 14 cards each, there are 21 Major Arcana, plus (usually) the separate Fool card to contend with. Does one cut those out? Or does one, with some ingenuity, factor them into the rules as well?
A freshly-dealt game of Cnidarian Solitaire. The first Major Arcana card, The Magician, has already been automatically moved to its foundation.
Cnidarian Solitaire, the product of Bruno Dias (available as pay what you want from itch.io), adapts Freecell rules to a complete, 78-card tarot deck, Fool and all. In addition to the four suits (in this case not the popular Smith-Waite suits, but aquatic versions: Boughs, Fossils, Coral, and Shells), all 21 Major Arcana are also present, and The Fool which has Special properties. As is typical, there are four open cells which may hold one card each, though consecutive sequences of cards can be moved regardless how many are open. Since there is no distinction between Red suits and Black in a tarot deck, building tableaus only requires that each successive card be a different suit from the card beneath it (the suits are, helpfully, differently colored for each). The primary goal, of course, is to get all 14 cards of each suit to their respective foundations.
Major Arcana are handled much differently, however. Because each one is unique, they cannot build down on each other. But because they are numbered, they get foundation piles. There are 21 in total, with 3 piles shared between the lot: one starts at 1 (The Magician) and counts up, another starts at 21 (The World) and counts down, and the one in the middle starts with 13 (typically the Death card in tarot, but left deliberately nameless here) and can count either up or down, with the catch that you will need to pick a direction and commit to it for the remainder of the game.
Finally, there is The Fool, which bears no number and has no foundation to fit in. The Fool fills the role of a Joker, in Cnidarian; a wild card, which can be placed (in the tableau) on top of any other card, and have any other card placed on top of it. Cnidarian's rule set also allows for the entire sequence of cards, including the Fool itself and any sequence above and below it, to be moved as one whole stack, giving way to many unusual movement strategies once it's been uncovered.
The Taropedia offers deep, almost exhausting, insight into the design decisions and symbolism of every suit and Major Arcana card in the deck.
So, certainly, Cnidarian's rules are interesting enough, and the actual implementation in software is pleasant enough to use that I have no real complaints (not even about the lack of an undo function; see my Shenzhen Solitaire review for more about why that's not a problem). But what really stands out here are the card designs (from the public-domain illustrations of Ernst Haeckel's Artforms of Nature), and above even that, the Taropedia, a very well curated in game guide that not only explains every rule, but also every single decision that went into the artwork for the game's unique deck, and what all of the Major Arcana represent (in some cases, even comparing themselves directly to the Smith-Waite cards). The author describes the presence of the Tarotpedia as being born from their own love of in game codices and encyclopedias, which is a love that I can also claim to share. Its presence is highly appreciated, to say the least.
Cnidarian Solitaire can be found Right Here, for a minimum price of nil (higher amounts encouraged), and is available officially for Windows and Linux computers. I would also like to offer a hat tip towards Twitter user @RamessesXIII, who directed me towards this game in the first place. Y'all know what I like.