Gujin is a PC boot loader that can analyze your partitions and filesystems. It finds the Linux kernel images available, as well as other bootable partitions (for *BSD, MS-DOS, Windows, etc.), files (*.kgz) and bootable disk images (*.bdi), and displays a graphical menu for selecting which system to boot. It boots the Linux kernel using the documented interface, like LILO and GRUB, so it doesn't need any other pre-installed bootloader. It can also directly load gzipped ELF32 or ELF64 files, with a simple interface to collect real-mode BIOS data. There is no need to execute anything after making a new kernel: just copy the kernel image file into the "/boot" directory, with a standard name. Gujin is written almost entirely in C with GCC, and it fully executes in real mode to be as compatible as possible.
Coreboot (formerly known as LinuxBIOS) is a project that aims to replace the normal BIOS with a little bit of hardware initialization and a payload. Payloads can include a compressed Linux kernel, FILO, GRUB2, OpenBIOS, Open Firmware, SmartFirmware, GNUFI (UEFI), Etherboot, ADLO (for booting Windows and OpenBSD), Plan 9, or memtest86.
iPXE is a network boot firmware. It provides a full PXE implementation enhanced with additional features such as the ability to boot from a Web server using HTTP, and the ability to boot from a SAN using iSCSI, AoE, SRP, or FCoE. It supports a wide variety of network devices, including wireless and Infiniband networks. iPXE is an effective replacement for gPXE.
UPX is a portable, extendable, high-performance executable packer for several different executable formats. It achieves an excellent compression ratio and offers very fast decompression. Your executables suffer no memory overhead or other drawbacks. UPX supports vmlinuz/386, linux/elf386, linux/386, win32/pe, dos/exe, djgpp2/coff, and many more.
Syslinux is a collection of boot loaders for Linux and other operating systems which operates on Linux ext2/ext3 filesystems, MS-DOS FAT filesystems, network servers using PXE firmware, or from CD-ROMs. Syslinux has an advanced extension API and contains two optional menu systems. It also includes MEMDISK, a tool for booting legacy operating systems from non-traditional media like PXE or CD-ROM.
Kerrighed is a Single System Image operating system (SSI) for clusters. It offers the view of a unique SMP machine on top of a cluster of standard PCs. The goals are high performance of applications, high availability of the cluster, efficient resource management, high customizability of the operating system, and ease of use. It is implemented as an extension to Linux operating system (a set of Linux modules and a small patch to the kernel).
GRUB for DOS is a rebuild of the GNU GRUB boot manager for DOS, and can be run under real mode DOS. It also has many new features. It can be booted through BOOT.INI of Windows (grldr) and kexec of Linux (grub.exe). It can directly boot NTLDR (WindowsNT/2K/XP), IO.SYS (Windows9x/Me) and KERNEL.SYS (FreeDOS). The disk emulation feature is another enhancement over GNU GRUB, and can be used to run legacy DOS/Windows9x systems with floppy or hard disk images.
mbootpack is a tool that takes a Multiboot kernel and modules (e.g. a Xen VMM or a xen-linux kernel and initrd), and packages them up as a single file that looks like a bzImage Linux kernel. The aim is to allow you to boot Multiboot kernels (specifically, Xen) using bootloaders that don't support the Multiboot standard (i.e. pretty much anything except GRUB).