Apple has opened up the kernel source for OS X Intel Build:
The release of OS X's kernel source marks a huge step forward for developers. The source for the PowerPC version of OS X has been available for some time now, but developers had been eager to for the Intel source when Apple announced its transition last year. According to Apple's press release:
Source code for the kernel of Mac OS X 10.4.7 for Intel are now available. Several changes were made in order to publish the kernel (xnu) sources. As a result, the kernel built from these sources differs from the one found in the 10.4.7 software update. In order to accommodate these changes, several kernel extensions were also modified and must be downloaded and installed in order to run a kernel built from these sources on Mac OS X 10.4.7 for Intel.
More info at DailyTech.