Via https://links.imirhil.fr/?ZYvpXw

multicd.sh is a shell script designed to build a multiboot CD image containing many different Linux distributions and/or utilities.

Via https://www.tecmint.com/multicd-create-multiboot-linux-usb/

netboot.xyz is a way to PXE boot various operating system installers or utilities from one place within the BIOS without the need of having to go retrieve the media to run the tool. iPXE is used to provide a user friendly menu from within the BIOS that lets you easily choose the operating system you want along with any specific types of versions or bootable flags.

AIO Boot is an All-in-One bootable software for USB and HDD. Is one of the best Multiboot USB Creator for Windows.