Metalinks collect information about files in an XML format used by programs that download. The information includes mirror lists, ways to retrieve the file on P2P networks, checksums for verifying and correcting downloads, operating system, language, and other details. Using Metalinks details the Free Software programs you can use to download them with. There are also clients on Mac and Windows. With a list of multiple ways to download a file, programs can switch to another method if one goes down.
Full story: Slashdot | Metalinks Tries to Simplify Downloads