[iseyler]

How about 31 bytes?

http://www.returninfinity.com/baremetal-helloworld.html

Why use ELF or Linux? Flat binaries (and a custom OS) to the rescue! :)

[Someone]

Why limit yourself to an OS? Design your own instruction set, with a single-bit 'hw' instruction!

As with all games (even Nomic) a game is only a game if there are rules that limit what one can do.

[kpreid]

The esoteric language HQ9+ does this.