Justinmind Prototyper is a tool to design wireframes and run simulations for web, desktop and mobile applications. The product looks similar to Axure, and lets you define user interface elements using a drag and drop environment with component libraries, and attach actions to components. The prototypes allow you to map interactive behaviors to elements, define process logic and flow, and add functional specifications and annotations.
Looks very full featured and offers the possibility of running a web server to deploy multiple prototypes that are viewable in a browser and allow users to comment on designs. The product is priced for Enterprises, and cost is prohibitive for individuals, but may be of interest to larger companies. Trial versions are available for Windows or Mac OS.