winevdm came to mind as a rather different Windows API + CPU emulator project - it glues WinAPI thunking to MAME's x86 emulator to run Win16 apps against the Win32 API. On 32-bit x86 this is redundant, because the built-in WoW32 will do the same job. winevdm enables running Win16 apps on 64-bit Windows on x64 and ARM.
CPU Emulator
wine based Win16->Win32 conversion codes:
Relay routines from 16-bit to 32-bit are autogenerated by convspec
DOS emulation for Win16
16-bit <=> native HANDLE conversion
Fix compatibility problems, fix compatibility problems
It's a wonderful project. Allowing me to run a 30 years old Win16 companion program (for a HP 53310A frequency domain analyzer) on modern 64bits Windows.
The closed Github issues are a trip. https://github.com/otya128/winevdm/issues?q=is%3Aissue+is%3A...
In the words of its own README: