Selenium Grid is a framework to run test distributed over a range of test devices. It's used for testing web applications. Its possible to write tests in different popular programming languages, including C#, Groovy, Java, Perl, PHP, Python and Ruby. The tests can be run against a range of webbrowsers on platforms like Windows, Linux, and OS X.
It is open-source software, released under the Apache 2.0 license: web developers can download and use it without charge.