After installing this script to a webspace it is capturing all incoming requests and forwards them internally to a single configured website passing back any response from that external website. Thus it is transparently mirroring a website to be available under a different URL.
In addition to basic forwarding the script features internal cookie management so the external website's cookies aren't stored in browser of clients using the proxy's URL.
This tool might be used to move a website to a different server/hoster while keeping domain registrations e.g. to keep running an existing e-mail infrastructure. In addition, this proxy is useful to circumvent ad blockers running on clients' browsers by integrating external ad server content into your own website's namespace/domain. Finally you might want to use this tool to hide the fact that a web application is available under different port, e.g. if you are working with Ruby On Rails making your web application available on port 3000 by default, but you want to make it accessible without selecting different port.