Booting from USB
Modern computers can boot from USB storage like disks and sticks. You may even try to boot from a digital camera if you like. This article shows how to install Linux on a USB disk so that you can boot from it.
Multibooting means installing more the one operating system or distro on the same drive which can be a USB flash drive or USB HDD.
Persistence means the can store files on the flash drive and your setting so they will be available on next booting from the flash drive.
If you are using Windows
UNetBootIn
UNetBootIn allows you to install a Linux of your choice to a USB disk. You will need internet connectivity or a CD/DVD image to be converted.
Can be used for Multibooting.
Can create a LiveUSB with persistence which means you can store files and settings on the USB drive and keep them after rebooting.
Etcher
Doesn't support UEFI Systems
Rufus
UEFI compatible.
UUI:Universal USB Installer
Not compatible with UEFI systems.
download from here [1]
YUMI:Your Universal Multiboot Installer
It can be used to create a Multiboot Bootable USB Flash Drive containing multiple distros on the same drive.
Download YUMI from this link
Win32 Disk Imager
Works on Windows 7/8.1/10.
Ventoy
Easy2Boot (E2B)
SARDU
Supports both Legacy BIOS and UEFI. https://www.sarducd.it/
If you're using Linux
UNetBootIN
Can be used for Multibooting.
Can create a LiveUSB with persistence which means you can store files and settings on the USB drive and keep them after rebooting.
To install UNetbootin from the Ubuntu PPA, run the commands:
sudo add-apt-repository ppa:gezakovacs/ppa sudo apt-get update sudo apt-get install unetbootin
Etcher
Doesn't support UEFI Systems .
To install Etcher on Ubuntu see this.
Startup Disk Creator (in Ubuntu)
In standard Ubuntu (Gnome desktop): press the square of dots on the left south side of the screen the search for "Startup Disk Creator" (without the quotes).
Your flash drive will be sdx where "x" is the number of your flash drive according to the system. It is better to choose your USB flash drive by its size.
In other flavors of Ubuntu such as Kubuntu-Lubuntu-Xubuntu-Ubuntu Mate-Ubuntu Budgie: open the main menu then type "Startup Disk Creator" (without the quotes).
USB Image Writer (in Linux Mint)
From the main menu search for "usb image writer" (without the quotes).
MX Live USB Maker (in MX Linux)
Available in the distribution MX Linux.
Mkusb on Ubuntu and Linux Mint (advanced)
Can be used to create persistent usb drives.
For a detailed guide see this
Command line tools (advanced)
MultibootUSB (Advanced)
Ventoy
Easy2Boot (E2B)
SARDU
Supports both Legacy BIOS and UEFI. https://www.sarducd.it/