A group project worked on in CodeFellows using socket.io and d3.js. The idea of the app is to look for changes to a webpage supplied by the user and only update the user's view when changes have been made to that site.
It will also show you how many other people are viewing the page using d3. We used web sockets to update the number of users viewing the page in real time and to be able to update the user's view instantly.
Here is the address of the site: f5yourself.herokuapp.com