Password Composer is a companion app for the Greasemonkey script / Google Chrome extension that generates unique password for websites based on your (singular) master password and the website's domain name.

The app deliberately doesn't store your password or previous websites for security reasons.

Greasemonkey script: http://userscripts.org/scripts/show/1341
Google Chrome extension: https://chrome.google.com/webstore/detail/password-composer/piepponjhmpppjdllplegiagclpkncbf