What low level / systems programming do you do?

Hashnode seems to represent the market as a whole so far, by a wide representation of front end web developers, fewer backend developers, and even fewer system programmers. Representing the smaller group of sysadmin/operations oriented coders as well as the hobbyist low level tinkerers, I'd like to hear what interesting things you do that is closer to the hardware and infrastructure. I'm sure there are tons of creative yet not yet mainstream solutions and projects being developed that we could all gain from learning about.