If you're a developer, adding Metalink support to Open Source programs and getting projects to use it for their downloads will be a huge help. Examining the source code from current open source Metalink clients and generators could be useful.

Current open source Metalink clients (downloaders) 

• aria2 (Cross Platform, C++).
• libmetalink (C library)
  
• wxDownload Fast (Cross Platform, C++).
• Free Download Manager (Windows, C++).
• Phex (Cross Platform, Java).
• Appupdater (Cross Platform, Python).
  
• Metadl (Windows, C++).
• DownThemAll! (Cross Platform Firefox Extension, Javascript).
• Metalink Checker (Cross Platform, Python). It can also be used as a library as it is in GGet.
  
• KGet (Cross Platform, C++).
• Mini Downloader
• easyMule
  

Current open source Metalink generators:

• The MirrorBrain
• MirrorManager (Python)
  
• Metalink Editor (Cross Platform, GUI, Python).
• Metalink tools (Unix/Windows, C++).
• Metalink Library for PHP and Python (metalink-library) (Cross Platform, PHP, Python)
  
• Geo McFly (Unix/Windows, Python).
• Simba (Unix, Perl).
• RoPkg::Metalink / Metalink @ Packages Resources (Unix, Perl).
• cURL (Perl).

Metalink is useful to Free and Open Source software. It was designed for community projects that use multiple mirrors and P2P. There is a whole ecosystem of applications, sites, and projects involved in Metalink.

We invite other Download Managers, Web browsers, BitTorrent clients, and other P2P programs to support Metalink.

Ideas:

We didn't get accepted for GSoC 08, but these ideas could be good starting points for newcomers. Please familiarize yourself with our project and software, and come up with ideas of your own. Please join our discussion list and post about your ideas! 

Complete: Check out Appupdater 1.0!  

Design and create a friendly, easier to use GUI for Appupdater, which provides advanced functionality to Windows, similar to apt-get or yum on Linux.

Difficulty: Easy

Skills: Python coding, familiarity with UI/design issues.

Mentor: Neil McNab (Appupdater / Metalink Checker author)

Details: Get ideas from the better GUI package managers/updaters on Linux.

Complete: Neil has added .jigdo -> .metalink converter/downloader to Metalink Checker. 

Jigdo with .metalinks and Metalink downloader.

Difficulty: Easy.

Skills: Bash scripting for Jigdo, C++ for aria2 or other (if needed).

Mentor: Tatsuhiro Tsujikawa (aria2 author)

Complete: GGet uses Metalink Checker for metalink downloads!

GNOME/GTK GUI for Metalink Checker / Download Manager integrated into the GNOME Desktop

Difficulty: Medium ( Accepted for GNOME GSOC! )

Skills: Python coding, familiarity w/ UI/design issues

Mentor: Neil McNab (Appupdater / Metalink Checker author)

Details: Implement the features of a modern GUI download manager. Metalink Checker is written in Python and can be used as a library.

Complete!: MirrorManager now supports Metalink, added by Matt Domsch.

Integrate Metalink generation into Fedora's MirrorManager

Difficulty: Medium

Skills: Python coding

Details: Coordinate with Matt Domsch, MirrorManager's maintainer. Discussion on fedora-devel & fedora-infrastructure.

"Mirrormanager doesn't store files in it's database, only directories, so that has to change first. That means adjustments to the crawler etc. I've managed to generate a few working metalinks out of TurboGears, only thing that's missing is checksum information. I have to talk to Seth Vidal to see if I can integrate the torrents, that's a separate script atm, based on an .ini file"

Debian has accepted a GSOC project which is similar, a Javascript Jigdo client. Presumably, it could be adapted to use .metalinks.

Details: Jigdo uses wget currently for downloads. If aria2 was used instead, it could download multiple files from multiple mirrors at one time, making the download faster and spreading load between mirrors. "Jigsaw Download, or short jigdo, is a tool designed to ease the distribution of very large files over the internet, for example CD or DVD images. Its aim is to make downloading the images as easy for users as a click on a direct download link in a browser, while avoiding all the problems that server administrators have with hosting such large files." Info on using aria2 with jigdo.

Difficulty: Easy to Medium.

Skills: Depends on project.

Details: Drupal proposal: posts, blogs, new thread. Peter Poeml has added metalink creation to the openSUSE download redirector! Matt Domsch added it to Fedora's MirrorManager.

Custom solutions for specific projects like Debian, CentOS, Eclipse, VLC, etc.

Difficulty: Easy to Medium.

Details: We'd expect you to do this for multiple projects (5-8), as each will be a small amount of work

Native axel (download accelerator) support. 

Difficulty: Easy to Medium. 

Skills: C coding. 

In progress: Tatsuhiro has released libmetalink, a C Metalink Parser. But this will also require some axel specific code. Someone who works on Axel plans to do this.

Details: Metalink support might require adding XML & checksum library dependency.

High Definition video downloads made faster/error free with Metalinks

Difficulty: Medium to Hard.

Skills: JSpeedStreamer written in Java, Metalink Checker in Python.

Mentor: Neil McNab (Appupdater / Metalink Checker author)

Details: Could integrate with JSpeedStreamer or use Metalink Checker.

KGet: work on Metalink improvements and integrations with rest of KDE (Nepomuk, Kgpg)

Difficulty: Medium

Skills: C++ coding

In progress: KGet team is working on part of this but could use help.

Details:Add support for download repair, integration of BitTorrent/FTP/HTTP multisource downloads, pass digital signatures in Metalinks to KGpg, let Nepomuk acquire metadata for semantic desktop. KGet GSoC ideas list.

Integration with Bouncer which serves up files for OpenOffice.org, Mozilla, & Gentoo

Difficulty: Medium to Hard.

Skills: PHP 

In Progress?: Bram submitted a patch which has not been merged yet. 

Details:  "Bouncer is a database driven mirror management app that has three main components - a bounce script, a sentry script to check mirrors and files for integrity and a set of web-based administration tools."

  Bouncer already has a database filled with information: hash, urls, preferences, etc. However, the bouncer project is trying to keep it's mirrors in shape by using a spider and checking the downloads against the real files.

By serving up metalinks, you can keep the work of the spider down and give the users more security.

Integration with Arch Linux's Pacman updater

Difficulty: Medium to Hard.

Skills: C coding.

Mentor: Tatsuhiro Tsujikawa (aria2 author)

Details: Arch founder Judd Vinet provided an early Metalink script on their forums. A good start for using aria2 can be at Faster Pacman Downloads and Improve Pacman Performance.

BitTorrent support for Metalink Checker

Difficulty: Medium to Hard.

Skills: Python coding.

Mentor: Neil McNab (Appupdater / Metalink Checker author)

Details: Metalink Checker currently supports only HTTP and FTP downloads.  We should be able to reuse code from other Python based Bittorrent clients and add support to Metalink Checker.  BitTornado looks like the best Python option out there.

Integration with FreeBSD ports infrastructure

Difficulty: Hard.

Contact: Unknown. Contact appropriate maintainers/mailing list to see if this is a possibility.

Details: "Metalink is a great concept which might be added to the ports infrastructure. Metalink files can be preprocessed in order to retain big mirror lists in bsd.sites.mk. Or an XML guru can convert bsd.sites.mk to an XML version and include it into metalinks in some way. Stub metalinks can be easily created for each port with a simple script.

At this time only www/aria2 has some Metalink support. Aria2 has a few dependencies, but it's completely unnecessary to cram it into the base system. FETCH_DEPENDS would work very nice.

Chunk checksum verification in DownThemAll! (Firefox Addon)

Importance: High.

Difficulty: Medium?

Skills: Javascript coding.

Native wget support.

Importance: High. 

Difficulty: Hard.

Skills: C coding. 

In progress: Tatsuhiro has released libmetalink, a C Metalink Parser. But this will also require some wget specific code.

Details: Metalink support is planned in a future version of wget, but it could be added earlier for single source (ie no multi-source) downloads, with hopefully the ability to failover to other URLs if a mirror goes down. You could also add other improvements to wget from their list. Co-ordinate with Micah Cowan (wget maintainer) on a patch.

wget GSoC list.

Native cURL support.

Importance: High. 

Difficulty: Hard.

Skills: C coding. 

In progress: Tatsuhiro has released libmetalink, a C Metalink Parser. But this will also require some cURL specific code. 

Details: Maintainer Daniel Stenberg writes:

A metalink file transfer library could be made as a layer on top of libcurl, and I think that is the only logical and sensible way.

Adding metalink support to the curl tool however, seems like a good idea to me…

Google Chrome support

Importance: High.

Difficulty: Easy to Medium?

Skills: C++ coding.

Bonus: Familiarity with libxml2, which Chrome already depends on.

Native Firefox support. 

Importance: High.

Difficulty: Hard. 

Skills: C++ coding.

Mentor: Ed Lee (Mozilla)

Bonus: Familiarity with Mozilla codebase.

Details: (This project was for Mozilla GSoC, was accepted, but the student chose another project). Firefox already handles XML & checksums so no added dependencies. The goal would be: Single source (ie no multi-source) downloads, checksum verification, and adding multiple files to the download queue.

A Metalink download system similar to the BitTorrent client / server architecture

Difficulty: Ambitious and extremely hard. :)

Skills: Up to you.

Details: See Ad-Hoc Metalink Swarms?, Mirror URIs & MetaMirror Servers