WinToUSB is the best free Windows To Go Creator that allows you to install and run Windows operating system on a USB hard drive or USB flash drive, using an ISO image or CD/DVD drive as the source of installation. 

WinToUSB's key features include:

• Easy-to-use wizard interface that provides step-by-step instructions for creating a Windows To Go USB drive.
• Creation of Windows To Go from an ISO image file or CD/DVD drive.
• Clone an existing Windows OS (Windows 7 or later) to a USB Drive as a Windows To Go Workspace.
• Use of a Non-Enterprise Edition of Windows 10/8.1/8/7 to create Windows To Go Workspace.
• Creation of Windows To Go on Non-Certified Windows To Go USB Drive.