This is a Facebook chat clone written using Strophe.js and Ember.js. You can see a short screencast here.
First of all you'll need a XMPP server e.g. ejabberd that can be easily installed using homebrew or apt-get. The widget does not handle user registration or subscriptions - these features will most likely be managed by your web application. If you want to try it out you'll have to create XMPP accounts and subscriptions between them yourself. The easiest way to do it is to use any IM chat client or via command line interface of your XMPP server (ejabberdctlif you're using ejabberd).
The widget runs on a web server written in Node that acts also as reverse proxy for XMPP server. It requires express and http-proxy packages. Run node server.js and it will start the server on localhost:9677. Sign in with any of the accounts you've created earlier and you should be good to go.