  http://techbase.kde.org/Development/Tutorials/Collaboration/HotNewStuff/Introduction

  the service which KDE uses to provide in app download possibilities for
  new and/or additional vocabulary files is called "Get Hot New Stuff -
  GHNS"...

  here the spec:

  http://ghns.freedesktop.org/spec/ghns-spec.html

   * Providers file: http://ghns.freedesktop.org/spec/ghnsproviders.xsd
   * Download file: http://ghns.freedesktop.org/spec/ghnsdownload.xsd

  some libraries, but non plain qt, or C++...
  http://ghns.freedesktop.org/software.php

  here the KDE implementation:
  http://ghns.freedesktop.org/knewstuff2/
  http://websvn.kde.org/trunk/KDE/kdelibs/knewstuff/

  Provider URLs (from parley:
  http://websvn.kde.org/trunk/KDE/kdeedu/parley/src/parley.knsrc):
  http://edu.kde.org/parley/newstuff/providers41.xml
  http://edu.kde.org/parley/newstuff/providers44.xml

  here on of the download xml files:
  http://download.kde.org/khotnewstuff/parley/parley.xml

  Parser with QXmlStreamReader proof of concept:
  http://www.gitorious.org/querymee/knewstuff

