There is!
https://itunes.apple.com/us/app/parallels-desktop-lite/id1085114709?mt=12
Mac and Linux cost free. Windows is where you pay.
Holy crap, I did not know that.
Well, to answer your question, I think that's the best bet for virtualizing macOS for free. If you come to want to virtualize Windows for some reason and want that to be free give VirtualBox a try. Windows virtualization on it is ok (not great, but ok).