Vagrant calls the backends "providers." It ships with 4 providers IIRC (VirtualBox, Hyper-V, VMWare, Docker), and there are plugins for dozens of others (it's so large a list because there's one provider each for pretty much every cloud service out there, even ones I've never heard of).

I think that VirtualBox and VMWare are the only two providers that work everywhere, unless docker runs on windows now.