key differences between Darwin & FreeBSD; Darwin & Mac OSX ?

[Nathan Vidican]

I know there there may be more appropriate places to post and/or ask, 
and I'm not asking for an advanced technical difference in terms of code 
or anything... but does anyone know some of the key differences between 
Darwin and FreeBSD, and/or the differences between Darwin and Mac OSX ? 
What does darwin offer that FreeBSD doesn't? Similarily, what does OSX 
offer that Darwin doesn't?

Any ideas, comments, suggestions, rtfm-referrals, and or links would be 
greatly appreciated.

--
Nathan Vidican
nvidican at wmptl.com (member of questions at freebsd.org, no need to cc)