Hmm, I imagine there are some out there. I get an email periodically from some company that does just that, remotely.
OTOH, I like to write my own stuff if I feel like I can afford the time. I don't know how big a project this would be, but could see sitting down with the manual and checking out is_file() and file_exists(), along with readdir() and some stuff to create something like that. FWIW, before someone jumps on the fact that those are just "local" functions, there's a user-made "URL exists" function at php.net/file_exists that uses fsockopen() to make a header call to a webserver and checks for category 200 responses....
