SeaBIOS on a Coreboot laptop is pretty minimal. Paltry CPU speeds on anything that supports it nowadays, but fun for a beater system.

Coreboot looks promising. Do you know why the CPU speeds are so bad? And do they get better once the main operating system starts up?

	▲	doublepg23 an hour ago \| parent [-]
		Not a hardware engineer so feel free to fact-check all of this. My understanding is Coreboot is a minimum-viable firmware implementation to get your hardware initialized ... and not much else. Once Coreboot is ready you then use "Payloads". Payloads can be as varied as booting into Linux directly, GRUB directly, or a whole UEFI/BIOS implementation. SeaBIOS is a whole FOSS BIOS implementation (commonly used for emulators like QEMU) and is somewhat tractable according to my prior research (~50k lines of C). My comment about CPU support is due to modern systems using UEFI - the payload for that is TianoCore EDK2. It's quite large (900k+ lines) and while it has much more eyes on it, if minimalism is what you're looking for I doubt it would qualify. That leaves you with systems from before ~2013 or so - assuming you can even flash Coreboot to them, which only supports a handful of systems. I suppose you could just jump into Linux though. Perhaps it's silly to do anything else.