Prototyping tools

Scott McDowell has written an article for Boxes and Arrows called Visio Replacement? You Be the Judge about tools for prototyping rich interaction designs. We recently adopted Axure here at Extractable and we’re very jazzed about the way it’s enabling us to do IA work and interaction design and tie together wireframes with sitemaps and process flows and then export them all as a clickable HTML prototype (even if the HTML is still spaghetti).
In this article Scott compares Axure with a number of other products, all of which he calls simulation tools (comparing them to aerospace simulations):

User experience professionals who leverage simulation technology are able to visualize projects much earlier within the development lifecycle, while producing requirements that are much clearer than those generated through traditional requirements gathering processes. In fact, two of these packages, iRise and Serena, were actually created to help business analysts visualize requirements when they didn