I've just come across Justinmind, a prototyping tool that at first glance looks similar to Axure. If this doesn't mean much to you, it's a way to prototype with a fairly simple drag-and-drop interface.
Pretty much like what you can do with Visio, but much, much cleverer.
I've never used Justinmind before, but am a big fan of Axure so I'm curious to see what it's like.
Justinmind is about to launch the beta of their latest version. They're offering the chance to win a fully functioning version (worth about $500) if you trial the beta and provide feedback.
Has to be worth a look at that price.
Justinmind blog with video demo
Review of Justinmind on uxmatters.com
Register to join in the beta trial and win a copy