FUN FACT: Libreboot was the first coreboot distro, starting in December 2013. It provides free boot firmware, replacing proprietary BIOS/UEFI.
It's a coreboot distro like Debian is a Linux distro. It provides a fully automated build system (source-based package manager) for compiling upstream sources.
Other coreboot distros have existed for a few years now.
https://libreboot.org/other.html
I've decided to promote them on Libreboot's website, as part of my general desire to promote free boot firmware.