Keep is a Node.js application that allows broadcasting slides made with reveal.js by using Socket.IO.
When the presenter changes the slide, all the attendants can see the current slide in real time.
The attendats can make an comment or question and the presenters will see on their screen.
You just need to run the file app.js using Node.js, and that's it.
You will have your app running into http://localhost:3000
In this app you can be either an attendant or a presenter. It also allows more then one presenter at a time.
You can see an online demo here: https://keepslides.herokuapp.com/