Libreboot provides boot firmware for supported x86/ARM machines, starting a bootloader that then loads your operating system. It replaces proprietary BIOS/UEFI firmware on x86 machines, and provides an improved configuration on ARM-based chromebooks supported (U-Boot bootloader, instead of Google’s depthcharge bootloader). On x86 machines, the GRUB and SeaBIOS coreboot payloads are officially supported, provided in varying configurations per machine. It provides an automated build system for the configuration and installation of coreboot ROM images, making coreboot easier to use for non-technical people. You can find the list of supported hardware in Libreboot documentation.