Gummiboot is German and means Rubber boat - I am not sure where that comes from
Gummiboot is a simple UEFI boot manager which executes configured EFI images. The default entry is selected by a configured pattern (glob) or an on-screen menu.
It is simple to configure, but can only start EFI executables, the Linux kernel EFISTUB, UEFI Shell, grub.efi, and such.
It needs an EFi System Partition (ESP) to load and that should be on /boot.
These are early days and I don't think anybody is using systemd version 220 yet - but the idea is probably to make the UEFI install as seamless as possible.