Operating systems that support Multiboot
The following operating systems are known to support out-of-the-box the Multiboot specification to boot their kernels. This simplifies their boot process in machines with multiple operating systems installed because there is no need to chainload their native boot loaders (if any); GRUB is all that is required.
Feel free to add any other operating system that supports Multiboot to the list below; just keep it sorted alphabetically.
AROS.
NetBSD since the 4.0 release.
ReactOS The freeldr.sys bootloader can be directly loaded and run as a multiboot kernel