This repository contains disassemblies of the "BIOSes" found in Sega Master System consoles. These are built-in ROMs which do some intialisation of the system, then check the various connections for a valid game and boot them. In most respects they are not really BIOSes, more like initial program loaders, although many also have built-in games.
You can read more about them at http://www.smspower.org/Development/BIOSes.