Statless and system agnostic

I've often wondered how one would write an adventure that was statless and system agnostic.

I'm not entirely sure it's doable, or at the very least useable.

I know there are a few books out there that were produced well that are decent.  I also know there are a lot that paint the picture of being agnostic but still have kinda sorta dnd stats in them.

There are others that have their own baked in system and notes about conversion.

I think writing source and campaign style books is a lot easier to do.

Do you have any favourites that check off the box of being statless and system agnostic?