FreeBSD's netgraph
I was looking around at some different Bluetooth implementations when I stumbled across NetGraph (graph based kernel networking subsystem).
http://www.freebsd.org/cgi/man.cgi?query=netgraph&sektion=4
It sounded very nice (reminds me of the MediaKit) when reading about it, so I just wanted to draw some attention to it.

Comments
Re: FreeBSD's netgraph
Very interesting link, indeed.
I guess many past or present Haiku net team members had once thought and talked about building a more modular, dynamic, BeOS-ish network stack. Because quick and dirty porting a "classic" BSD net stack is no fun these days, and sounds "outdated design" at time too.
Others BeOS coders did/do try also to experiment this "graph" approch too. Nathan Whitehorn in Glass Elevator context had explored a C++ one, which I tried to adapt to our C-only constraint under the src/tests/kits/net/new_stack subtree.
BTW, BONE have a kind of graph design too...
Maybe, one day, we'll find at last enough time to finish these experimentations and write a better designed net stack. Hope is always there.
So, big thanks for the link.
FreeBSD's netgraph
Actually, I thought it was old news after I posted it seeing the line 'It first made its debut in the main tree in FreeBSD 3.4'. Anyway it sounded to cool not to be mentioned and now I'm glad I did.