I recently wrote a program to allow NetBSD to boot other OS' from within 
NetBSD itself.  It only works on Technologic Systems boards (TS-7xxx) and 
requires no specific kernel support other than read/write access to /dev/mem 
and /dev/kmem.  This is a port of a program I did for Linux.  It makes a 
little more sense on TS's default Linux since it only takes 1.1seconds to 
boot Linux + initrd, but this is still useful on NetBSD IMHO.

ftp://ftp.embeddedARM.com/bootload.nbsd

I wrote it because I don't like writing or using complicated bootloaders 
(GRUB, RedBoot, uBoot, etc...) and having to write two versions of device 
drivers (one for the bootloader, one for the OS).  There are many clever 
uses for this as it basically allows you to write your own bootloader with 
all the functionality of  NetBSD in as little as one line of shell script.

I'll probably implement arbitrary ELF file loading sometime this month 
(right now it only works with raw images)

Here's some documentation I previously wrote when announcing the Linux 
version, but equally applys to NetBSD:

http://tech.groups.yahoo.com/group/ts-7000/message/4511
http://tech.groups.yahoo.com/group/ts-7000/message/4520


//Jesse Off