I want to have pong board on a big screen and users connecting to it using their mobile.

I know I need to learn websockets, anything else? Any recommendation? The simple as possible with less third party libraries as necessary so I can actually full understand it. Its mostly for my own learning :)

Google experiments has a nice list of examples but no tutorials:

https://chromeexperiments.com/mobil...

@g-m-f sorry, forgot to mention I want to do everything Web based.. Just a (big!) detail I forgot lol

meteor.js should do it.

If you like .net i would say signalr, check out shootr.net

@heyheni Yup. Try meteor or loopback

www.meteor.com is a javascript framework with an integrated mongo database on clientside and serverside for instant live action web apps. You can use it with "Blaze" meteors way of javascript wich is pretty standard js and quite easy to use. Or with Angular js or React.
The cool thing is you can verry easy specify what runns on the client and what on the server. Together with the Iron Router you can run a site on your billboard and individual ones for the clients. Oauth login with facebook is built in which makes it easy to collect emails for marketing purposes. :)

Thanks everyone and special thanks to @heyheni for such detailed response! Hey @dfox, when can we start giving rant golds (similar to reddit gold) to people? :D