It's FOSS - https://itsfoss.com/multiple-linux-one-usb/
Brief: This tutorial shows you how to install multiple Linux distributions on one USB. This way, you can enjoy more than one live Linux distros on a single USB key.
I enjoy trying out different Linux distributions via live USB. It gives me the option to test the OS on a real hardware, not in a virtualized environment. Also, I can plug in the USB to any system (read Windows), do whatever I want and enjoy the same Linux experience. And yes, in case something goes wrong with my system I can use the USB drive to recover!