No one questions that 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.
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