Mao (https://en.wikipedia.org/wiki/Mao_(card_game)) is a logical deduction and social card game. Players, when they win (or by taking turns), add rules known initially only to themselves. They then enforce these rules; it is the job of the other players to determine, based on the pattern of enforcement, what the rules actually are. For example, a rule might require players to say "have a nice day" when a seven is played, or penalize players for looking away from the deck of cards when it is their turn.
Good Mao rules:
Are fun. "[X] player wins" or "mix up the deck every time someone plays a king" are not fun rules; "players picking up their own penalty cards receive an extra card" is.
Can be deduced purely from the patterns of enforcement within the game, although this should be difficult; rules that require signing every card you play with a secret private key are not fun.
Check the Wikipedia page for more information, if you're curious; feel free to ask questions for clarification.
I will award the bounty to responses according to how fun I think the rules are. More, better rules means more bounty.
1,000Part of the default rules I play with is that if you can't play anything and draw a card, if that new card is playable, you can play it immediately and end your turn. A rule I like to add is that when that happens, you have to say "The chairman is generous" or something along those lines. It's super simple, but surprisingly difficult for the other players to guess because they're used to looking for rules based on the identity of the card played, and the draw-then-play-immediately pattern is so familiar that no one thinks twice about it.