Libreboot is a coreboot distro like Debian is a Linux distro, but replaces proprietary BIOS/UEFI. It provides an automated build system (source-based package manager), providing easy to use releases.
I posted a link to this page earlier:
https://libreboot.org/other.html
Between them all, a substantial portion of coreboot is covered. I've asked the other projects to link to other distros as I have to them. This is part of my general desire to promote free boot firmware.
Federation of coreboot distros.