YUMI (Your USB Multiboot Installer) is a multiboot USB boot maker or media creation tool that can be used to make a multisystem bootable flash drive. This utility helps you quickly create a custom multi bootable USB drive containing several different ISO files.
The Universal USB Installer (Imager) aka UUI is a Live Linux bootable USB maker software. This ISO to USB imaging tool helps users easily make a flash drive bootable and as a result, boot from USB.
Boot Multiple ISO from USB using GRUB2 from Linux. Here is one way to manually create a Multiboot USB Flash Drive (Multiboot ISOs) from a running Linux environment.