Not sure why it was posted, but intro amd64 assembler code is frustratingly rare.
I've just started learning assembly, but my main platform is FreeBSD/amd64 so none of the basic tutorials run on my machine. 99.5% of such code is for i386, and 99% of the unix code is for Linux. I set up a FreeBSD/i386 jail for running the few basic intros for the platform, and I've been using a CentOS/i386 VM for the tutorials in that platform.
This link brings my personal count of unix amd64 assembler "Hello, world!" pages to three. While I don't think the submission is really noteworthy, I am glad I caught it here.