I have an idea for a website, and I plan to hire someone to build it. Is there software that I can use to "sketch" how the pages will look so I can give these to the person I hire for them to work from? Ideally I want something that allows me to design all of the pages and have them linked together as I intend. However, I don't need the software to build the site or do the HTML behind it. It's just to do the appearance and the coder will work out how to make the site.

What is this kind of software called? It's not an HTML editor. The only thing I can think of the moment is MS Paint!