Hey so I'm one of the team that built this app - we're super stoked to have pulled it off over the weekend. We focussed on trying to build the best UX for annotating and commenting on pictures/images/screenshots/wireframes as well as a super easy flow to signup and get started. Heavy reliance on raphael.js for the canvas work and rails obviously on the backend.
Would love to get comments/feedback from the HN community. Once judging is over we'd love to package it up - tidy up the loose ends and put it in a permanent home.