Yes, we tried server-less system on WebRTC. The problem is an actual support for WebRTC in mobile browsers. It is even less than HTML5. So, just wait for a moment.
It is server-based. Server-less version will be later as I wrote. Yes, it is like chat rooms, it is like client-server and it is like web. There is a web session actually :). We've tested a way for linking (pairing) two devices. From HTML5 there is File Reading API
Do you just send the message to the server and back to the other client?
How is this different than chat rooms we had 10 years ago?