Metalink

Metalink is a cross-platform and cross-application Internet standard/framework/file format for programs that download, including download managers, BitTorrent clients, Web browsers, FTP clients, and P2P programs. For increased convenience, the multiple download locations for a file (FTP/HTTP/P2P) and other metadata in HTTP header fields and/or an XML file with the extension .meta4 or .metalink. The duplicate download locations provide reliability in case one method fails. Some clients also achieve faster download speeds by allowing different chunks/segments of each file to be downloaded from multiple resources at the same time (segmented downloading).

Other features include automatic hash verification of finished downloads, automatic repair of downloads with errors, listing multiple files to be added to a download queue, and automatic OS/language selection.

Metalink is extensible, and supports listing multiple partial and full file hashes along with PGP signatures. Most clients only support verifying MD5, SHA-1, & SHA-256, however. Besides FTP and HTTP mirror locations and rsync, it also supports listing the P2P methods BitTorrent, ed2k, magnet link or any other that uses a URI.

Read more about Metalink:  Development History, Client Programs, Client Libraries, In Use, Metalink Client Feature Comparison, Metalink Generation, Example Metalink 4.0 .meta4 File, Example Metalink/HTTP Header Fields, Example Metalink 3.0 .metalink File