Darwin (in case you didn’t know) is kernel of Mac OS X, IOS and other Apple operating systems. It’s open source. I thought that was weird when I found out because Apple isn’t an open source company. It uses code from BSD systems and most open source licenses require derivatives to be published under the same license as the original work. As you probably know, BSD systems use the BSD license.
Mac OS X actually has several open source components (unlike Windows) you can get the source for stuff at http://opensource.apple.com. It is also the world’s best-selling UNIX-like system. I don’t know if it meets the FSF’s definition of “Free Software”.
I don’t no that much about Mac OS X. I’ve only spent about 20 minutes of my entire life in front of a Mac and most of that time was spent playing with Garage Band. 
All I know is UNIX is awesome and therefore, Mac OS X must be.
The Darwin logo looks like the BSD daemon except it’s a platypus. It’s name is Hexley.
