Retrocomputing is the current use of older computer hardware and software. Retrocomputing is usually classed as a hobby and recreation rather than a practical application of technology; enthusiasts often collect rare and valuable hardware and software for sentimental reasons.
https://solhsa.com/z80/index.html
Building a game for the Spectrum from scratch in Z80 using sjasmplus
Pretty comprehensive documentation of the Gameboy's hardware and that of related peripherals (eg the Gameboy Printer).
http://nhiro.org/learn_language/repos/EDSAC-on-browser/index.html
