http://selenium.openqa.org/
Selenium is a test tool for web applications. Selenium tests run directly in a browser, just like real users do. It runs in Internet Explorer, Mozilla and Firefox on Windows, Linux, and Macintosh, Safari on the Mac.
http://www.joedog.org/JoeDog/Siege
Siege is an http regression testing and benchmarking utility. It was designed to let web developers measure the performance of their code under duress, to see how it will stand up to load on the internet.
