KDE on Cygwin is the port of Qt and KDE desktop environment (both of which are commonly distributed natively in Linux operating systems) to Windows using Cygwin, the POSIX emulation layer for Windows, and the Cygwin XFree86 server. It helps Wintel computers to run applications originally created for the above frameworks by providing the functionality that the applications expect of the combination of KDE and Qt in a manner transparent to the original programs—an example of the core principles of the concept of emulation. GNOME is already available on Cygwin.
The KDE on Cygwin project is no longer being actively developed in anticipation of a natively-compiled version of KDE 4 for Windows.
The project was started by Ralf Habacker in May 2001. Its goal is to ensure compatibility of major programs that were originally only available through the act of starting up a computer with a Linux Live CD containing the KDE environment, or an actual installation of a Linux distribution. As with many emulation examples, not all the common KDE programs are guaranteed to work unmodified on KDE on Cygwin due to the complex interaction of all the components that are expected of full Linux distributions but not provided by the KDE on Cygwin project. The open-source nature of KDE and several of the programs running on it allows the number of these shortcomings to be found and circumvented in order to provide working programs for Windows that prior to their porting, may have worked only through X11 ports made for Cygwin, lacked a graphical interface altogether having to run at the command line, or were completely non-existent on Windows.
The project has ported various KDE and Qt versions, and are of beta quality.
The KDE on Cygwin project also started developing a free version of Qt/Windows called Qt/Windows Free Edition.