Let me just say right off the bat, that I hate, hate working on Functional Specifications, and the reason for my loads of loathing is the user interface (UI). Managers want specifications to include screenshots of the UI, but as I’ve tried to explain, it is a chicken-and-the-egg situation. Do you want a specification, or do you want me to work on the UI?
The answer to this problem is usually creating wireframe mockups of the eventual UI. However, I’ve yet to find a mockup tool that I like. I’ve tried tools like Visio and OmniGraffle which are good tools, but they focus more on diagraming and process flow than wireframe design. Not to mention the aforementioned applications share a particular trait with an almost standard for creating mockups — Axure — complexity. The barrier to entry for these applications for doing something as simple as creating mockups is relatively high. I have longed for something simple, powerful, and straight-forward.
And then I found Balsamiq Mockups.