Uno is based on an open source card game.
"Rule #1. It’s forbidden to tell the rules of Mao.
Rule #2. There are two exceptions to rule #1, which are rule #1 and rule #2."
This is how Mao was introduced to me. Very fun game
(Actually I watched an ongoing game of Mao before I joined the party and started playing. As I was watching the game I understood a rule and said it out loud, not knowing I wasn’t supposed to say the rules. This, of course, granted me a penalty at the beginning of my first game.)
Mao Club Rule 1: You don’t talk about mao club.
Mao Club Rule 2: YOU DO NOT TALK ABOUT MAO CLUB.
Mao Club Rule 3: Someone yells stop, goes limp, taps out, the game is over.
Mao Club Rule 4: Only two guys to a game.
Mao Club Rule 5: One game at a time Fellas.
Mao Club Rule 6: No Shirts, No shoes.
Mao Club Rule 7: Games will go on as long as they have to.
Mao Club Rule 8: If this is your first night at mao club, you have to play.
I played this once. It’s very fun
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Both uno and crazy eight are mentioned on the wiki as being related to mao.
Because these games have so many local variations people who play while traveling may not know the local rules, eventually shaping the existence of Mao. Many of the more common mao variations follow similar rules and structure.
Sounds like Mornington Crescent with more steps…