Coreboot lets you replace your proprietary closed-source BIOS with a modular, flexible open-source alternative capable of booting a wide range of flexible payloads on emulated and physical hardware.
I have always been a fan of the FORTH based OpenBoot on Sun SPARC hardware, also known as the “ok” prompt.
You can build and run your own X86 “ok” prompt with OpenBIOS:
Ix OS Payload with SeaBIOS
Ix is a baremetal standalone OS implementing a ZZ-structure navigator.
Not having a bare metal machine to run it on at the moment I wanted to play with it - I built one with QEMU and CoreBoot for fun.
I did not have a quick and easy grub box to boot it with, so I used QEMU and coreboot.
First, git Ix from github and build according to docs to get ixmage.elf.
Ix Source (github)
Second, git coreboot from coreboot.org and build with make crossgcc.
How To Build Coreboot
Now make menuconfig to configure a 2MB ROM image, add SeaBIOS and a vgabios as a payload.
Next use coreboot's build/cbfstool build/coreboot.rom add-payload -f ixmage.elf -n img/Ix
Customize SeaBIOS with splashpage and additional payloads (coreboot)
build/cbfstool build/coreboot.rom print to see the coreboot, seabios, vgabios, and Ix
Run with qemu-system-x86_64 -L build -serial stdio -bios build/coreboot.rom
Press F12 in SeaBIOS to boot custom payload and choose the img/IX option from the menu
Ix boots and runs quite well - I was able to follow along with this video directly in the QEMU window side by side with this video:
Ix Demo (youtube)