I can think of a bunch of stuff that has moved or is moving from third party crates into the standard library: parking_lot, hashbrown, (minimal) Future trait. But I agree that no crate has moved wholesale into the standard lib.

parking lot and hashbrown moved their internals, replacing ones that already existed. This is probably a distinction that doesn’t actually matter but in my head it’s different for some reason, thanks for pointing it out :)