http://multibootusb.org/page_download/

Stuck at “Installing Syslinux…”?

source: https://github.com/mbusb/multibootusb/issues/361
https://github.com/mbusb/multibootusb/blob/master/data/tools/gptmbr.bin

and saving in under

/usr/share/multibootusb/data/tools

You may need this:

sudo apt-get install qemu-kvm qemu virt-manager virt-viewer