Realistically you want virtualbox, which is closed source and proprietary. qemu will run Linux but I don't think it's accurate and performance enough to run windows, right?
You can run a Windows VM with QEMU, but virt-manager is probably a simpler choice. Qemu is very accurate and performant, but also very flexible and not exactly straightforward to configure. But if your goal is to experiment with virtualization and learn, either one is probably a better choice than VirtualBox.
If security/isolation of unknown not quarantined code, Windows would not be high in my list as a sandbox.