GRUB is the GRand Unified Bootloader.  Briefly, bootloader is the first
software program that runs when a computer starts. It is responsible for
loading and transferring control to the operating system kernel software
(such as NetBSD orLinux).  GRUB understands ffs, FAT{16,32}, ext2fs,
ReiserFS, minixfs, and VSTafs.  It can directly boot NetBSD, FreeBSD,
OpenBSD and Linux without any other bootloader, loading a.out and ELF
kernels from the disk and passing along necessary arguments (in most cases). 
It can also boot any operating system (the above, plus eg Windows, OS/2) by
chaining to that operating system's specific loader.  Grub features a
runtime command line and loads its configuration at boot rather than
requiring rerunning of a separate utility.  Other features are TFTP booting,
serial console support, large disk support, support for both DOS MBR label
and BSD disklabel simultaneously, booting from hard drive or floppy.

GRUB is available for the i386 architecture only.