WinToUSB (also called Windows To USB) is the best free Windows To Go Creator which allows you to install and run a fully-functional Windows on external hard drive, USB flash drive or Thunderbolt drive. It is so easy and efficient, with just a few simple steps and a few minutes, you can create your first portable Windows 10/8/7 directly from an ISO, WIM, ESD, SWM, VHD, VHDX image file or CD/DVD drive, or you can use it to clone existing Windows OS installation (Windows 7 or later) to USB or Thunderbolt drive as portable Windows. WinToUSB also supports creating Windows installation USB flash drive from Windows 10/8/7/2016/2012/2010/2008 R2 installation ISO file, with it you can install Windows from the USB flash drive easily.
Free vs Professional vs Enterprise | Comparison
Note: A licensed version provides more features, and in order to get your hands on those features buy a license to support the software developer.