Before UEFI, IBM ThinkPads had an odd implementation of "secure boot", whose purpose I never really figured out (was digging into the BIOS for something else and just happened to notice it in passing, then dig a little bit of RE on) that acts as a hypervisor too.

It's a ROM module with the strings "IBM V86" and "Secure OS boot support ROM", neither of which search engines seem to find any results for (perhaps deliberately?); neither now nor the roughly a decade and a half ago that I attempted to research it. This might now be the only reference to such a thing on the increasingly forgetful Internet.