What framework used by links search engine?

There's lots of links search engine growing nowadays:

http://www.uploadcity.com/
http://rapiddigger.com/
http://www.filecrop.com/
http://www.filestube.com/
http://www.general-search.net/

...and lots more...

Do you know what framework (zend framework? django? pylons? rails?, etc...) used for building that search engine?

----added----

and what framework capable for building that search engine?

I suppose a different framework for each of them.