Apps with 'Create Multiboot USB' feature

Ventoy is an open source tool to create bootable USB drive for ISO files. With ventoy, you don't need to format the disk again and again, you just need to copy the iso file to the USB drive and boot it.

The YUMI exFAT (Your Universal Multiboot Installer) media creation tool can be used to automatically create an exFAT bootable USB flash drive containing multiple operating systems, antivirus utilities, disc cloning, diagnostic tools, and more.

MultiBootUSB is a software to create multi boot live Linux on a removable media i.e USB disk. It is similar to UNetbootin but many distros can be installed, provided you have enough space on the disk.