Apple has updated the Darwin source code to version 6.6, bringing it to parity with OS X 10.2.6. Darwin is the open source base of OS X. The very short blurb from Apple:
Darwin 6.6 Source Code Posted
The Darwin team is pleased to announce the immediate availability of the Darwin 6.6 source code corresponding to Mac OS X 10.2.6. Darwin and a number of other projects are available via Web DAV (as well as regular HTTP). Also, access to the CVS repository has been updated. [May 14 2003]
You can get more information at Appleis Darwin site. There is as yet no other specific notes on the update.