mbootpack (Multiboot kernel and modules)

This is a tool that takes a multiboot kernel and modules (e.g. a Xen
VMM, linux kernel and initrd), and packages them up as a single file
that looks like a bzImage linux kernel. The aim is to allow you to
boot multiboot kernels (in particular, Xen) using bootloaders that
don't support multiboot (i.e. pretty much anything except GRUB and
SYSLINUX). This is, as you might expect, pretty grim stuff, involving
lots of lovely 16-bit real-mode code.
