http://watir.com/ is an open-source Ruby library for automating web browsers. You can use it to run automated tests on your web application or even to load test your application.
I haven’t used it yet but I can see how it could be useful, running a number of concurrent browser threads on a VPS, performing a set of actions on your website/app, putting it through it’s paces, even triggering Ajax requests. You could have Watir running on a cluster of machines and really challenge your website.
If I ever put it to good use I’ll be sure to write about it further.
A couple useful links:
http://www.benhallbenhall.com/2012/02/user-performance-monitoring-watir/ someone talking about using Watir for load testing
http://wiki.openqa.org/display/WTR/Examples examples of Watir usage