The KDE (K Desktop Environment) Project is building an integrated desktop environment including a window manager, file manager/web browser, and other components using the Trolltech "Qt" toolset, a development toolset written for C++ that allows applications to be deployed atop either X11 or Win32.
KDE had been using the MICO CORBA ORB to construct an application embedding framework known as KOM and OpenParts. According to the [ KDE-Two: Second KDE Developers Conference], they found themselves unable to use the standardized CORBA framework, citing problems with concurrency, reliability and performance, and have instead decided to create Yet Another IPC Framework involving a shared library called libICE.
On the other hand, the KDE Technology Overview for Version 2.0 provided a somewhat different story, so it's not completely clear just what is going on; they indicated the use of an IPC scheme called DCOP, with that as a layer atop libICE, with the option of also using XML-RPC as an IPC scheme.
Even moreso than GNOME, KDE parallels the X.org's desktop environment called CDE.
People commonly, and incorrectly, claim that KDE is "a window manager." KDE is most definitely not a window manager, any more than GNOME is.