I am thinking that this would be an Apache server with some custom pages, or possibly a java application. Used for browser or http client testing, it should give me a variety of 500 errors when a specific page is requested. Give me a page that responds in 5 seconds, 10, 30 or whatever. Give me a page where the first byte does not come back for 30 seconds. Give me a page where I get a few bytes per second.
I expect that others have made this kind of thing before, and I know it is not too difficult, but I would certainly like to use what someone else has already made.