Links

kernel.org
mailing lists on kernel.org (main communication platform for kernel devs)

osdev.org

lowlevel.eu (german)

kernelnewbies.org (not that great, but didn’t want to leave it out)

tcpipguide.com

Jonas Berlin VGA initialization

Chris Giese VGA initialization

C++ Reference (best I know – I use it all the time)

gnu.org tutorial on inline assembler

Graphics File Format Specifications (archived)

A list of very informative – or at least interesting – YouTube Videos

A list of puzzle-games on steam, that I find interesting for nerds.
Also a list of surreal games on steam, that may be off topic here, but anyways.