I don't want to derail the comments on this post too much, but it's called Notado (another commenter has already linked it) and I have posted about it a few times on HN before (all in my submissions history).
There are quite a few high-quality discussion threads on those previous posts that are worth checking out if you're interested in learning more!
There are quite a few high-quality discussion threads on those previous posts that are worth checking out if you're interested in learning more!