This is a bookmarklet that you use to generate passwords for web sites. The passwords are generated based on the URL and a master password that you supply.
Pretty cool.
From the web site:
I hate passwords. I mean, I don’t mind making up and memorizing the really important ones but what about all those e-commerce and community sites that want me to create accounts? I used to end up using the same password at all of them and then I felt stupid knowing that one SQL Server exploit or disgruntled admin could cost me my whole identity.
So, I wrote a bookmarklet to make up passwords for me. It asks for my master password, which is all I have to remember, and uses it to make a unique password for each site. It even types the password into any password fields on the current page for me, whether I’m registering for a new account or logging in on a subsequent visit.