The second stage boot loader is the one that usually loads the boot image. This it does by fetching the boot image from the TFTP server, and loads it in an OS specific manner. It is planned that the OSKit libexec.a library's a.out and ELF loader will be used to actually load the image.
Future versions of Nilo would allow this loader to also be a menu that then loads the real boot loader. This allows for user input to select which OS to boot. This would then invoke the correct loader as another stage.
The second stage boot loader is the one where the higher-level protocol support is. This is where NFS or a disk based file system can be used in addition to TFTP for loading files.
To support loading the boot image, a ramdisk will also be created of the appropriate type.