Imagesource: https://github.com/asmboy4gb/

At what point can a machine actually be called self-sustaining? Opinions certainly differ quite a bit here. But what you basically need, is an assembler, an editor and the possibility to permanently store source code as well as binary output on some storage medium.

Everything else like compilers, libraries, frameworks, TCP/IP stacks, and 42 additional layers of problems can then be implemented by oneself without further ado merely with the help of enough available lifetime to waste. And Voila ... a self-sustaining machine.

Can this be done on a Gameboy? An unknown creator posting as Asmboy4gb and probably going by the name Andreas not only proved this, but also released the related project. At Asmboy4GB the name itself says it all. Programming for the Gameboy on the Gameboy.

Why hasn't anyone thought of this before? Lovely.