Well, in case it helps anyone else I am using Freemind.

It is “mind mapping” or brain storming software, I know, I know. I thought the same but I read a website that said how good it was for piecing together disparate projects. I have to say that it is very simple to use and it has helped me already.

It helps me to see all of the bits of my idea in one place, and I can connect things. It has already saved me loads of paper.

I hope it helps someone else.