I think this needs some more explanatory text. It's a nice quick mockup generator, it would appear, but it oddly exports not HTML, but rather a nodeJS application, which seems insanely heavyweight for a simple form builder.
It looks like links and forms can be linked inside the mockup generator, and it's that linking that they are trying to preserve by exporting a node.js app. I'm not sure that I'd care enough, to lock things in in this fashion, but perhaps it's a nice tool if you are already planing an app using Node/Express
I don't think it's so much to keep working on the prototype afterwards, but to be able to export it out of the tool (Napkin) and still be able to easily show someone your prototype.
