VirtualBox: Oracle supports an open source virtualization app known as VirtualBox.

Fusion supports the installation of many different operating systems, including Windows, Linux, and macOS. VMWare Fusion: Fusion is the Mac virtualization app offered by VMWare - a leader in virtualization tech.Parallels supports a wide range of guest OS, including Windows, Linux, and Mac. Parallels: The first to bring virtualization to the Mac.There are three primary virtualization apps for Mac: But unlike Boot Camp, both the Mac operating system and the guest operating system run at the same time. As a result, the guest operating system running on the virtual machine does not run as fast as in Boot Camp. Virtualization on the Mac makes use of a software layer called a hypervisor to emulate all of the underlying hardware. Virtualization abstracts the hardware layer, making it look like each operating system has its own processor, RAM, graphics, and storage. Virtualization allows several operating systems to run on computer hardware at the same time. Performance tuning and customization needed to achieve the best performance.

Mac osx emulator on win 7