It depends on what you are building. I try to start every project as a mvp. Minimum features minimum screens minimum and short delivery dates. For mvps we usu

It depends on what you are building. I try to start every project as a mvp. Minimum features minimum screens minimum and short delivery dates. 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. That usually evolves with more slides to more witeframy-ish sketches with annotations. As a rule we never spec more than a couple of screens and functions. 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. We test on users, get feedback, and start again.