Metalink files are simple XML files that download programs read and make use of for easier segmented downloads, among other things. It also has checksums and other info.:
<?xml version="1.0" encoding="UTF-8"?>
<metalink version="3.0" xmlns="http://www.metalinker.org/">
<files>
<file name="ubuntu-6.10-desktop-i386.iso">
<os>Linux-x86</os>
<size>732293120</size>
<verification>
<hash type="md5">b950a4d7cf3151e5f213843e2ad77fe3</hash>
</verification>
<resources>
<url type="http"
location="ro"
preference="90">
http://ftp.iasi.roedu.net/mirrors/ubuntulinux.org/releases/.pool/ubuntu-6.10-desktop-i386.iso
</url>
<url type="http"
location="jp"
preference="100">
http://ftp.yz.yamagata-u.ac.jp/pub/linux/ubuntu/releases/.pool/ubuntu-6.10-desktop-i386.iso
</url>
<url type="http"
location="us"
preference="90">
http://ftp.osuosl.org/pub/ubuntu/.pool/ubuntu-6.10-desktop-i386.iso
</url>
</resources>
</file>
</files>
</metalink>
Linux Kernel .metalink (XML) file
RFC 5854 describes Metalink.
http://tools.ietf.org/html/rfc5854