WinToUSB's key features include:
Easy-to-use wizard interface that provides step-by-step instructions for installing Windows/WinPE on a USB drive.
Install Windows/WinPE from an ISO image or CD/DVD drive.
Support for Windows 7/8/8.1/10 Technical Preview/2008 R2/2012/2012 R2 and WinPE 2/3/4/5.
Use any edition of Windows 8/8.1/10 Technical Preview to create Windows To Go USB drive.
Support for MBR and GPT disk layouts.
Don't need install WAIK (Windows Automated Installation Kit) or WADK (Windows Assessment and Deployment Kit).

Important notes:
Windows 7/2008 R2 does not have built-in USB 3.0 support, so Windows 7/2008 R2 will have to be booted from a USB 2.0 port.
USB flash drives are very slow. It takes a long time to install and run Windows from a USB flash drive, highly recommend using a USB hard disk or Windows To Go Certified Drives.
Windows To Go drives can be booted on different computers, so you can carry it to anywhere and use it on any computer.
Windows 7/2008 R2 is not completely portable. You may have activation and driver problems when booting on different computers.
You need to be an administrator on the computer you are installing the WinToUSB on.

Whats New:
Version 2.2 (2015.7.13)
MBR-based Windows To Go USB drive support booting both BIOS-based and UEFI-based computers
Clone current Windows OS (Windows 7 or later) to a VHD file on a USB drive
Clone current Windows OS (Windows 7 or later) to a USB flash drive
Sector by sector clone Windows OS to a USB drive
German language support