BridgeOS
bridgeOS is an embedded operating system created and developed by Apple for use exclusively with its hardware. bridgeOS runs on the T series Apple silicon processors and operates devices such as the OLED touchscreen strip called the "Touch Bar", Touch ID fingerprint sensor, SSD encryption, and cooling fans.
At boot time, the bootloader executes the bridgeOS kernel, then the bridgeOS kernel passes off to
the UEFI firmware.
bridgeOS is based on Apple's watchOS.