These files make up a collection of very cheap and messy PHP scripts meant to look like a vulnerable Web application. They were originally created to help with quick functional testing of the Watcher Web security tool set of rules. Each file in turn represents one test for one Watcher check. By loading the index.html file you will be presented with a list of all tests hyperlinked for quick loading.
WARNING - INSECURE PHP SCRIPTS
As if you couldn't tell by now, these PHP files are meant to mimic a vulnerable Web application. Of course they're very shallow, and nothing even close to a proper vulnerable Web application meant for real testing. Some of those that come to mind are DVWA, bodgeit, and well a whole bunch of others listed here.