So, Etherpad is a thing (actually, Etherpad Lite, which is a NodeJS thing). That is, a real-time collaborative editing tool. Essentially the answer collaborative web-based text editors, free and open source. Last year a WebRTC hook and plugin was made available for Etherpad (!!).
WebRTC is real-time communication for the web.
Earlier in March, 2015, Firefox 36 release came with the Hello feature of WebRTC calling (Firefox account needed, only). That is pretty cool and some say that Firefox is trying to steal thunder from Skype for Web, which Microsoft is supposed to be rolling out with WebRTC support (kind of).
In any case, this is actually a bit lame since the whole concept of browser-as-phone still requires a switchboard-based server connection rather than peer-to-peer. However, running one's own server, now that smells like freedom.
Turns out this is already available as Vetherpad.