As a very excellent virtual machine software with very high performance under Mac OS, VMware Fusion (Pro) is the best way to seamlessly run Windows on a Mac computer. It provides the ultimate Windows experience on a Mac OS, enables you to directly run Windows, Linux, Android or other OS at the same time without having to restart your Mac OS.
QEMU (short for Quick Emulator) is a free and open-source processor emulator widely used on GNU/Linux platform, written by Fabrice Bellard from France. It primarily converts the binary code written for a specific processor to another through a special 'recompiler', so as to realize the OS virtualization.
As a well-known application virtualization tool - i.e. the single-executable/portable software builder, VMware ThinApp is actually the former Thinstall Virtualization Suite which was later acquired by VMware. It can also be simply interpreted as one packaging suite for software and its complete running environment.
MoleBox Virtualization Solution (MoleBox VS for short) is a real-time software visualization/distributing tool with not perfect but professional and complete functions. It can package some software on Windows along with all of its auxiliary/necessary data and components into a single executable file (EXE), which can run the same as before or even faster.
As a completely free and lightweight (less than 5 MB) software virtualization/packaging tool for Windows, Enigma Virtual Box is capable of packing all the relevant files/folders of some software into its main program (main input file, supports both 32-bit & 64-bit EXE files), thus makes it to be a single-executable/portable app for most Windows versions (2000 or later).
There have already been the well-known commercial software VMware Workstation and open source freeware VirtualBox in the field of virtual machine, but in deed, Microsoft actually already has its own virtualization technology - Windows Virtual PC, despite it is a little old and only supports Windows 7.
VirtualBox (now, its full name should be Oracle VM VirtualBox) is a powerful cross-platform, open-source and x86-based virtual machine (VM) software. It allows users to virtual other x86-based operating systems on 32-bit or 64-bit Windows, Solaris and Linux operating systems, that is to say, the user can install and run Solaris, Windows, DOS, Linux, OS/2 Warp, OpenBSD or FreeBSD system as the client operating system in VirtualBox.