Apple Developer Connection: Darwin Releases
   Official page with downloads of the various Darwin releases and developer tools.
   http://www.opensource.apple.com/darwinsource/

Darwin Developer Documentation
   Programming in the Darwin kernel and information on the differences between Darwin and other BSDs.
   http://developer.apple.com/documentation/Darwin/Darwin.html

Fink
   A package manager for Darwin based on the Debian apt-get set of tools. 2900+ ports listed.
   http://fink.sourceforge.net/

Getting Started With Darwin/x86
   A helpful guide to getting and installing Darwin on an x86 system.
   http://darwin.monkeyvoodoo.net/

Hexley the Platypus
   The mascot of the Darwin OS.
   http://www.hexley.com/

Open Software in a Commercial Operating System
   A paper written by Wilfredo Sánchez, the then Open Source Engineering Lead at Apple, about the use of open source in commercial software such as Mac OS X Server.
   http://www.mit.edu/people/wsanchez/papers/FREENIX99.html

The Challenges of Integrating the Unix and Mac OS Environments
   A paper on the design issues Apple faced when they ported the Mac OS to a semantically different Unix base (Darwin).
   http://www.mit.edu/people/wsanchez/papers/USENIX_2000/

The GNU-Darwin Distribution
   A Unix distribution which focuses on the porting of free software to Darwin and Mac OS X.
   http://www.gnu-darwin.org/

XDarwin: X Windows on Darwin and Mac OS X
   A general overview of the project to bring XFree86 (X11 server) to Darwin and Mac OS X as well as pointers to download and mirror sites.
   http://www.xdarwin.org/