WebPagetest is an open source project that is primarily being developed and supported by Google as part of our efforts to make the web faster.
WebPagetest is a tool that was originally developed by AOL for use internally and was open-sourced in 2008 under a BSD license. The platform is under active development on GitHub and is also packaged up periodically and available for download if you would like to run your own instance.
The online version at www.webpagetest.org is run by for the benefit of the performance community with several companies and individuals providing the testing infrastructure around the globe.
In exchange for running a testing location, partners get their logo associated with the location and a banner on the site. Hosting a test location is open to anyone who is interested and does not constitute an endorsement of the services offered by the partner (however, I think you will find that the partners providing test locations tend to be very involved in the web performance community).
If you are having any problems or just have questions about the site, please feel free to contact me.