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That is the goal for the rest ones. Gnome.org is the main portal of Gnome and runs WordPress.
Bugzilla.gnome.org is the place that you file Gnome bugs. It runs bugzilla but Gnome Team think to completely remove it because Gnome has none bug -jk :)
Build.gnome.org shows the building status of Gnome applications. It runs buildbot.
In Git.gnome.org you can get all the latest Gnome packages, in source format of course. It runs cgit.
Mail.gnome.org hosts the mailing lists of Gnome. You all can involve here and contact developers, ask things you want to know or anything else. Registration takes 20 secs. It runs mailman.
Live.gnome.org is the absolute place if you want start Gnome developing. It is simply amazing! It runs moinmoin.
In my opinion it is great that Gnome Team decided to update the outdated sites.