I'm looking for the best tool to allow me to quickly put together a 2D game that relies largely on networking. It's extremely likely that this game will require a server side program to constantly run. I have little experience with these things and since it's a prototype i'd like the easiest options for achieving this.

I am looking to make this game for the web and mobile devices, although at present I only have access to ios hardware, (no android etc).

I just want to get the bare bones of this set up so I can test it from the earliest opportunity to see if it's fun.

EDIT - doesn't unity have some inbuilt networking stuff in it?