I'm not sure I understand what it is exactly, the page mentions QEMU so I assume it's emulating a PC and booting Windows on it? So does it mean that they've compiled QEMU for a Javascript target and packaged it in Electron?
If so, does it mean that it's a generic PC emulator in electron that can run any kind of PC-compatible software, including other OS?
It’s based on v86, so yeah, pretty much.