I just compared the result from rankit.free.fr and iwebtool.com and they are exactly the same. I used 9 of my websites project for comparing Eheh i would suggest this one http://www.searchengineengine.com/ But its better to work hard on the site
In theory, couldn't someone use the theories on Google's logarithm to actually calculate PR? Crawl the backlinks, and calculate how much power they are giving ect. It wouldn't be easy and it would probably be extremely resource intensive, but it might work.
It might work but you will have to create another kind of algorithm calculating the PR algorithm in live, i think if we can see it evolves in direct, i'm sure it's changing all the time from 1 to 50 000 and coming down, and again and again...