Coreboot is an open source firmware platform designed to replace the proprietary BIOS firmware used in most computers. It is designed to be fast, secure, and flexible, and to provide the ultimate control to users over their system's hardware. Coreboot can be used to boot an operating system from a variety of hardware platforms including x86, ARM, and RISC-V. It is highly customizable, allowing users to customize their boot process, as well as to add additional features and optimizations to their system. Coreboot is used in many embedded and Internet of Things (IoT) devices, as well as in some high-end servers and workstations. It has been used in a wide range of projects, including the Libreboot project, which is aimed at creating a fully free and open source computing platform.
Discontinued In May 2015, gummiboot was fully integrated into systemd to form its systemd boot component that serves as a UEFI boot manager. Following this action, the gummiboot source code repository was emptied in July 2015. - https://en.wikipedia.org/wiki/Gummiboot_(software)
Discontinued No recent developments, project site is archived.
GRUB
PLoP Boot Manager
Libreboot
gummiboot
Chameleon Bootloader
Chimera
XTIDE Universal BIOS
SeaBios allows you to boot from other bootable devices, unlike Coreboot. I have a Chromebook, but I couldn't boot my USBs from it, so I put my Chromebook in developer mode and installed SeaBios! My USBs are working fine now!