Just came across Jumpchart. Looks like a very handy tool for planning websites. Doesn’t look like it can handle designing serious interaction for an RIA, though. I’m also not sure how well it scales up. If you have a 10,000 page site, you might not want to plan it out with this program.
Still, if anyone has used this, I’d like to know. Or better yet, invite me to use it.
EXPERIENCING INFORMATION 
http://webworkerdaily.com/2007/10/25/another-approach-to-free-collaborative-site-prototypes/#more-1251
I think this tool and service is pretty cool.