The latest version of the Internet Draft of the Metalink Download Description is at http://tools.ietf.org/html/draft-bryan-metalink
(Incremental updates are at http://metalinks.svn.sourceforge.net/viewvc/metalinks/internetdraft/ )

Implementations:

• aria2
• Metalink Checker 5.0 - Will autodetect v3 and v4 format files and do complete conversions in both directions.
• Metalink Editor 1.3 - Will open v3 and v4 format files and do complete conversions in both directions.
• Web service to do minimal conversions for old clients.  Send your old download client to:
  
  http://www.nabber.org/projects/metalink/webconvert/?url=http://example.org/my.meta4
  
  This website spits back the contents of http://example.org/my.meta4 in
  Metalink 3.0 format.  Note: This also accepts a POST variable ("data") so that files stored on local drives can be converted.  XSL transformation files to do conversions are also available, this could be an easy way to add support for v4 in existing clients if the XML library supports XSL.
  

Known issues:

• None.
  

Ideas:

• None.
  

Changes from current Metalink specification:

• Different namespace:  xmlns="urn:ietf:params:xml:ns:metalink" (Previous: xmlns="http://www.metalinker.org")
• Different file extension: .meta4
  
• Different date format: RFC 3339. Example: 2008-12-13T18:30:02Z
• <metalink> attributes (published, origin, generator, updated) are now elements.
• <url> no longer has type attribute listing ftp, http, bittorrent.
  
• New <metaurl> instead of URLs to torrents or metalinks.
• Piece checksums are no longer numbered.
• Removed extraneous empty container elements: <files>, <verification>, <resources>
  
• Deprecated elements (<changelog>, <tags>, <mimetype>, <relations>, <releasedate>, <mulitmedia>, <screenshot>, <upgrade>, <bittorrent>, others?) and attributes ("maxconnections").
  
• IANA registry Hash Function Textual Names defines values for hash types. The SHA hashes now have a "-" in them: sha-1, sha-224 sha-256, sha-384, sha-512 instead of "sha1" etc.
  
• IANA registry Operating System Names defines values for OS types. This registry would need to be updated.
  
• Relax NG compact schema included.

Previous issues:

• Section 4.2.14 - Current Metalinks are limited to including PGP signatures of files listed inside the Metalinks, but not other types of digital signatures.  (This does not concern signing of Metalinks themselves, that is covered in the Securing Metalink Documents and Security Considerations: Signing sections).
  

     We could describe other types of file signatures, besides PGP, to be referenced in Metalinks.

     Current usage documented. For instance, this openSUSE Metalink contains a PGP signature.