To verify Meson's suitability for different types of projects, its developers do experimental build system conversions. In all simplicity it means that random projects are chosen and their build system is rewritten in Meson. Usually these are not fully polished ports, but should contain most of the work necessary to use Meson as the new build system.
Here is a list of projects that have had a build system port done.
* [QtCreator](http://lists.qt-project.org/pipermail/qt-creator/2014-May/003584.html), and a [followup](http://lists.qt-project.org/pipermail/qt-creator/2014-May/003598.html) on unity builds