From Hasleo Software:
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 operating system on an external hard drive or a USB flash 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 a CD/DVD drive, or you can use it to clone an existing Windows OS installation (Windows 7 or later) to a USB drive as portable Windows.