From the Hardware 2.0 mailbag: Can you install Ubuntu on a USB flash drive?Yes, yes you can. Here's how.

But you can also download an ISO file for any of these operating systems and for many other Linux distributions and use the tool to copy the files to your USB flash drive.

Installation type Now, you can choose your preferences, such as the language and the installation - we recommend selecting Normal installation. Confirm your choices by clicking on Continue. Do not ...

How to make your own bootable macOS 10.14 Mojave USB install drive All you'll need is a Mac, the Mojave installer, and an 8GB USB drive or SD card.

To Dual Boot, say Windows and Ubuntu, on separate Hard Drives, you must first meet the prerequisite and then follow the steps mentioned here.