iPod App for Brainstorming

I just learned about an app called SimpleMind used for brainstorming from the Teaching in the 21st Century blog.  (That's a quick screen shot of what it looks like.)  This link includes a write up about how it was used in this particular class as well as some of the teacher's observations.  Here is a link to the SimpleMind website.  I plan on getting the express edition for free to see how it works.