GRUB - Multiboot boot loader
EasyBCD - EasyBCD is NeoSmart Technologies multiple award-winning answer to tweaking Windows bootloader.
coreboot - coreboot is an extended firmware platform that delivers a lightning fast and secure boot experience...
U-Boot - Das U-Boot (the Universal Bootloader) and Embedded Linux
Grub2Win - Safely dual boot Windows and Linux without touching the Windows MBR.
Libreboot - Libreboot is a distribution of ...