This is Emu 
The X65 Computer Emulator.
Emu is based on chip emulators by Andre Weissflog.
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.
This emulator started as a hard fork of C64 emulator example and it shows in places - it is still a work-in-progress.
Fedora:
dnf install libX11-devel libXi-devel libXcursor-devel mesa-libEGL-devel alsa-lib-devel
Ubuntu:
apt install libx11-dev libxi-dev libxcursor-dev libegl1-mesa-dev libasound2-dev
Build using CMake and a modern C/C++ compiler.
Install Emscripten toolchain. Next, run the following commands:
mkdir wasm
cd wasm
emcmake cmake -DCMAKE_BUILD_TYPE=Release ..
cmake --build .
Linux
> build/emu --help
Usage: emu [OPTION...] [ROM.xex]
> build/emu roms/SOTB.xex
Windows
> build/emu.exe file=roms/SOTB.xex