vPerformer

VPerformer is quite a comprehensive tool to check and manage the performance of any webapp and all the elements that affect it.

With it you can check whether there are outside elements having a negative impact on how well your webapp works.

The application's graphic interface also means that it's easy to use, even if you don't have any programming experience. However, if you want to develop your own scripts (which is recommended), you should have a basic knowledge of JavaScript.

VPerformer is a fairly interesting tool for web administrators who have a decent amount of experience. Beginners might find it a little complicated, though there is a pretty thorough tutorial available when you begin.