Multiboot Specification

The Multiboot Specification is an open standard originally created in 1995 and developed by the Free Software Foundation. The specification describes a method of loading various multiboot kernels using a single compliant boot loader. GNU Hurd, VMware ESXi, Xen, and L4 microkernels all need to be booted using this method. GNU GRUB is the reference implementation used in the GNU operating system.

The latest version is 0.7.

Read more about Multiboot Specification:  Compliant Software