There is a card game called "Spot It!" that uses this concept. It is great fun to play with kids.

The math behind how you make a deck of icon-covered cards such that any two cards have exactly one icon in common is pretty interesting, ex: https://stackoverflow.com/q/6240113

I’m always a little disappointed in this because the answer is actually “they copied it from a textbook” rather than “they did some clever maths”. But I guess it’s a triumph of knowing what solutions exist and when to use them, rather than brute forcing a solution (which is one of the reasons I still think non vocational computer science education is essential).

The math behind it was covered by Matt Parker on Stand-up Maths: https://www.youtube.com/watch?v=VTDKqW_GLkw

Thank you for this really cool video! As a game designer, I find combinatorics super fascinating and helpful for creating balanced sets of cards or other variable content in my games. I wish I had a stronger foundation with it.

Note for anyone interested, this game is called ‘Dobble’ in Europe (or at least the UK and Germany).

Fun game.

Just a suggestion: accept clicks on a position area. At least for me, it didn't accept the click unless it was exactly on the letter's body (tricky during rotation)

Pretty cool. Got me entertained for a couple minutes.

I get “click the letter that appears in both circles”, two empty circles and some blank tiles at the top. Nothing responds to tapping. Am I missing something?

Firefox iOS.

EDIT works after a reload. Letters appear in the circles.

Finished the free play levels (up to 48), and enabled “crazy mode”. No idea what that does, and I couldn’t visually work out what effect it has (maybe the timer is faster?)

Very nice. I have to say I see games here I've tried and didn't like. This one was great!

It’s like Dobble!