Take the name of Debian and the first thing that comes into ones mind is a robust, user friendly Linux distribution which has helped spawn numerous other Linux distributions. But things have subtly changed. Recently, Debian team added two new architectures to Debian, namely - kFreeBSD for i386 and x64. That is right, Debian can now use the FreeBSD kernel. The tools surrounding the kernel are the same GNU tools found in Linux. So the end users running Debian with the BSD kernel won't find much of a difference in the feel of the operating system. But then, if you are running Debian using a FreeBSD kernel, you can seldom call it GNU/Linux .... you should call it GNU/kFreeBSD.
Source : Debian Announce List