Eyebrowse by MIT CSAIL Haystack Group
Eyebrowse enables real-time, serendipitous interactions with others that are on the same page as you. Using this extension, you can now converse with others on the web as well as publicly post messages to a feed, all within the confines of any page on the web.
To facilitate this, Eyebrowse allows users to automatically track and selectively publish what domains on the web they wish to be visible to others on. Just as in real-life, when you leave your private spaces, you can go out into your public spaces and bump into people and converse with them.