I know of at least one person who has a hack of The Quiet Year in progress! It's not out anywhere yet, but I've seen a draft - it's about building a cosmology, rather than a ground-level community, which I thought was a neat way to branch off of that.
Personally, I think my pick would be:
- Polaris: the way it structures the flow of play, and how players divide the control of characters between each other, is really interesting, and seeing the same kind of structure taken into different genres and in different directions would be neat. I know of one hack where the viewpoint was reversed, so that rather than playing a chivalric Knight, you played as the Mistaken, the threatening force, but I'm sure more could be done with it.