It depends on what you are building.<p>I try to start every project as a mvp. Minimum features minimum screens minimum and short delivery dates.<p>For mvps we usually take it from whiteboards to google presentations. We literally paste in a photo of the whiteboard and then add text boxes.<p>That usually evolves with more slides to more witeframy-ish sketches with annotations.<p>As a rule we never spec more than a couple of screens and functions.<p>Once done it gets handed to a dev (with an in-person briefing). They usually deliver something clickable in bootstrap which is great for web and mobile prototyping.<p>We test on users, get feedback, and start again.