Eleusis is a card game invented by the US American game inventor Robert Abbott in 1956. The name comes from the ancient greek town Eleusis, where the Eleusis mysteries were celebrated in honour of the goddesses Demeter and Persephone between the 16th century BC and the 4th century CE. The mysteries were rites kept secret to non-initiated, hence their name.
Here you can find the official page of the game. Eleusis is one of those great games that are quite unique, there are not many similar games. In this family we can find several Eleusis variants (such as EasyEleusis or Eleusis Express), as well as the party game Haggle (by Sid Sackson), the card game Mao, the chess-inspired Penultima, and the abstract games Jonash (by Pietro Gorini) and Zendo.
The aim of the game is to find out the hidden law of the game itself. And for this reason this game has a great didactic value to understand epistemology, gnoseology and the scientific method: experiences, hypotheses, counterexamples, false beliefs, conspiracy theories, and so on.
Here you can find the standard rules described in 1977 by Martin Gardner in Scientific American: Gardner_1977_NewEleusis
I played this game many many times, in game parties, at meetings of mathematical games and in the Eleusis Bot in Telegram. During the years I have improved many aspects of the rules, correcting some little problems, reducing chance, trying to make it fairer and more strategic. I called this new version Royal Eleusis, and here it is: RoyalEleusis. If you try it, please send me your comments. Enjoy!