I think RapidShare is a file sharing site a bit like MegaUpload. You don't get given a direct link to a file stored there, instead you get a link to a page which generates a download link for you after a given amount of time waiting, depending on server load. I'm assuming this leecher app saves you having to sit waiting for the page to generate the download link, and is able to start the download the second the link becomes available all by itself?