The BIOS in old Sun machined used to run some kind of Forth interpreter which would run code from your expansion cards to initialize them (not sure if that was meant to make this cross-platform/cross-architecture).

I vaguely recall trying to get an old SPARCstation to boot and figuring out how to work the Forth shell (which is similar to what Grub is now) -- http://en.wikipedia.org/wiki/Open_Firmware

That was one of the first "small factor" pizza box machines: http://en.wikipedia.org/wiki/Pizza_box_form_factor