Thanks sp0rk for the heads up.
Darwin is a version of the BSD UNIX operating system that offers advanced networking, services such as the Apache web server, and support for both Macintosh and UNIX file systems. It was originally released in March 1999. Darwin currently runs on PowerPC-based Macintosh computers, and is being ported to Intel processor-based computers and compatible systems by the Darwin community. Darwin is the core of Mac OS X. All software built for Darwin should be able to run unmodified on Mac OS X. However, because Darwin by itself does not encompass all of the features of Mac OS X, software that depends on higher-level features of Mac OS X (such as the Cocoa and Carbon toolkits) will not run on a stand-alone Darwin system. Now for the big news, Apple IS working on a version of Darwin for Intel processor based PC's. Form another source: Darwin/x86 has been around for a little bit now, and has had a few releases of binary Darwin distributions ready to install on x86 hardware. However, hardware support is still limited. Right now, Darwin must have IDE UltraDMA hardware, PS/2 Keyboard/mouse, VESA 2.0+ video card, and an Intel Ethernet adapter. Other hardware, such as AMD based machines, USB keyboard/mouse, etc are not supported. As you can see, Darwin for PC's has a lot of work that needs to be done and will not be out any time soon.
News source: TweakXP