Coreboot (formerly known as LinuxBIOS) is a free and open source BIOS/Firmware implementation intended to replace common proprietary BIOS firmwares.
In contrast to conventional BIOS it tries to initialize only the minimum required hardware (like RAM, PCI, serial) and leave the rest to a payload (which usually re-configures these parts anyway)
This payload can either be a conventional bootloader (like Grub2, FILO), a Kernel/ELF executable (like e.g. the Linux Kernel, memtest86, plan9 or etherboot) or some other Firmwares like UEFI, Open Firmware, OpenBios and SeaBios.
With this two-stage approach minimal boot times (<= ~1 sec on x86) and a small memory footprint can be achieved.
Currently over 230 Mainboards are supported and since a port from U-Boot coreboot know also supports the ARM architecture.
One pretty famous subproject is the flashrom tool that is often used to upgrade conventional BIOS on Linux.