KDE Plasma Workspaces is the top ranking desktop gui in pure robust features and asthetics.
It's one beautiful working environment. What is KDE written in?: Qt
Qt is the same framework used to create the Apps which run in the KDE desktop environment, the same framework used to develop the original KHTML, which was acquired and ported to WebKit by Apple.
Qt has a long history behind it and has evolved through the years and endured change of ownership several times over, now in the hands of Digia and under their governance via the Qt Project.
This advanced framework has a fine reputation using the Lesser GNU Lesser General Public License, which makes everyone in the open source community quite happy. The technology advancements put it on equal or, arguably, better footing than its competing GTk framework.
There was a period of uncertainty when TrollTech was purchased by Nokia, and the disposition of licensing was put into question. Fortunately, Nokia saw fit to find the LGPL acceptable.
So, today we see a trend with new Desktop iterations using Qt making recent appearances. First, Razor-Qt, then KLyDE, now we see a port of LXDE which uses the deprecated GTk2 framework is being made using Qt and will be named LXDE-Qt, appropriately.
It seems that gradually a stronger interest in Qt is being taken and, given LXDE's latest move, at least one Desktop which currently runs on GTk2 is hedging their bets and moving to Qt. They might have simply chosen to migrate to GTk3, but that wasn't done. Is the effort to migrate too steep of a climb? Apparently so. The LXDE community have done a great job setting up a wiki which addresses the technical challenges in migrating GTK projects to Qt--surely a big help to the community at large. Hats off to LXDE for doing that.
So, this is a very interesting trend indeed. Please take a look on the LXDE website to see how well the LXDE port has progressed. I will certainly try LXDE-Qt at the earliest opportunity.