A game about “technology trees”.
“Each technology in the game can only be unlocked once, but you need the entire tree completed to win.”
In other words, new technologies (“fire”, “printing press”, etc) are revealed each round (from a card deck, for example). Players bid money, then choose one technology in order of bid (highest -> lowest).
This, in itself, is incomplete. Obviously you can never win the game now! No player can get the full tech tree!
That’s why we add another rule.
You can get the missing technologies by trading!
If both players agree, they can “trade” technologies, which just means they both get the one they miss.
Additionally, you have a physical pawn that walks over your tech tree. The technology where it stands on your turn matters. (For your bid, for what you can trade, for a special action you have, something like that.)
Most importantly, if your pawn is on some space/branch, you can force other players to trade from that branch, to acquire the really hard-to-get technologies nobody wants to give to you.