A toolbox of 8-bit chip-emulators, helper code and complete embeddable system emulators in dependency-free C headers (a subset of C99 that compiles on gcc, clang and cl.exe).
Tests and example code is in a separate repo: https://github.com/floooh/chips-test
The example emulators, compiled to WebAssembly: https://floooh.github.io/tiny8bit/
For schematics, manuals and research material, see: https://github.com/floooh/emu-info
The USP of the chip emulators is that they communicate with the outside world through a 'pin bit mask': A 'tick' function takes an uint64_t as input where the bits represent the chip's in/out pins, the tick function inspects the pin bits, computes one tick, and returns a (potentially modified) pin bit mask.
A complete emulated computer then more or less just wires those chip emulators together just like on a breadboard.
In reality, most emulators are not quite as 'pure' (as this would affect performance too much or complicate the emulation): some chip emulators have a small number of callback functions and the adress decoding in the system emulators often take shortcuts instead of simulating the actual address decoding chips (with one exception: the lc80 emulator).