KDE isn't just the desktop environment these days! (In fact, the DE part of KDE is now called Plasma Desktop.)

The KDE project contains many applications, including ones you may have used, like Krita or Kdenlive. I think KCacheGrind also fills a quite unique niche on Linux, namely GUI profiling tools. But there are also many that stay more within the KDE ecosystem, like Kate (which is a pretty decent text editor) or Dolphin (the KDE file manager, and probably the most featureful mainstream Linux file manager). A lot of these applications are also decently cross platform and work fine on for example Windows, and even Haiku.

Also, KDE Gear (as the application suite is called) integrates many things quite nicely. For example, their LaTeX editor Kile is basically just a glued-together version of Kate and Okular (the KDE document viewer), with some extra stuff to work with all the LaTeX stuff. It means you get all the features of both, like Kate's quite good Vi mode, or Okular's capability to trim a document's margins.

Of course, KDE would very likely refuse to take "Kwimp" under its umbrella because they already have Krita, but even if you're not on KDE there may be some worthwhile applications that do fall under their umbrella. (Just like GNOME Boxes is an excellent choice for beginner-friendly virtualization, even if you're not running GNOME.)