I don't recall the name, but I remember using something exactly like (the originally intended) Backrub my first year in the dorms (1996 or early 1997). The program I was using was more of an overlay where you could draw on the page (using a simple MS-paint like UI) in addition to adding text annotations. You could either keep the changes local, or share them on some central site. It's downfall, as I recall, was threefold: buggy code, popularity, and the publicly annotated copies of popular websites turned into layer upon layer of graffiti. Something like the original concept for PageRank as mentioned would've been perfect.
It was a neat concept, but really only practical (as implemented) for the static web. It died long before dynamic page generation became widespread. (I just can't remember the name of it! :) )