You could try searching for software like this:

Load testing software -- can do things like download many video streams at once, to show you how well your server handles it. An open source example is Apache JMeter at http://jakarta.apache.org/jmeter/

Split testing software -- can compare and contrast different approaches to a web site, typically by creating two versions of a resource like web page A and web page B, then tracking which is most successful by whatever metric you want. Look at Bingo Card Creator by HackerNews user "paraschopra" at http://www.bingocardcreator.com/abingo/resources

System monitoring software -- can do things like graph your RAM and CPU over time, as well as let you script more sophisticated tracking like average CPU spike per connection. An open source example is Nagios at http://nagios.org/

Browser simulation testing -- can do automate click testing on your site, for example to create a test that pretends to be a user clicking on your links which run your javascript changes. An open source example is Selenium at http://seleniumhq.org/