Wikipedia
Xconfig
xconfig is short for the 'xconfig' target for the Linux Makefile. It is a graphical Linux compilation utility, which uses Qt. The xconfig utility is invoked by running 'make xconfig' in the base Linux source directory.
Qt has only been used since kernel 2.6. Kernel 2.4 uses a Tcl/ Tk configuration interface. A GTK+ interface (gconfig) is also available since kernel 2.6.