Windmill is a web testing tool designed to let you painlessly automate and debug your web application.
Windmill is no lnonger actively maintained, it has been eclipsed by Webdriver/Selenium 2. - I suggest, http://webdriver.io
Legacy Windmill is currently a very active work-in-progress so the best place to find up-to-date information would be online: http://wiki.github.com/windmill/windmill/
Another great location is the mailing list: http://groups.google.com/group/windmill-dev