Brienne Strohl mentioned a website called Gingko on facebook which allows you to write documents in the form of nested trees.

I've been playing around with it today and found it very useful, being able to write ideas out in a disordered way seems to get around some of my perfectionism issues and stop me procrastinating. The real test is whether I continue to use it in the future, I'll try to check back in a month or so.