As you might have noticed, I’m not much for documentation, especially stuff that sits outside of the application code base. For one thing, no one reads the documentation anyway (as the code is the source of truth), and for another, most projects follow the design-and-document-fully-only-to-build-something different approach.
However, one thing I do like are UI mockups. You can start with an intended UI and adjust as people “see” what is going to be built. Problem is, they have traditionally been painful to create (and take a lot of time). Balsamiq mockups addresses that problem by letting you create quick and simple wireframes that are easy to edit. It’s not free, but worth the money. Give it a try 🙂