From the makers:
"Layers is a new web platform that will launch in private beta in December.Sign up to be one of the first to try it out.
Users will be allowed in on a first come first serve basis. If you want to be among the first, sign up above using the code: create1108. We will contact you when you can start using it.
Imagine if you could pull a transparent layer over any webpage and then you could create upon it. You could annotate, draw graffiti, embed video, photos or do whatever you want. Then, by providing a link, others could see your layer (with the original content beneath it) and you could see layers created by other people. You could follow your friends and see all the layers they create. You could go to any webpage and see any of the layers that have been created over that site.
That's Layers. Welcome to the Vertical Web!!"