Here's how powerful OpenBoot is:

On a Sun, you can drop to OpenBoot via a key chord. If you type "go" from there, the OS will resume. This is usually 100% safe, even though your OS doesn't get run at all for the time you're in OpenBoot.

OpenBoot has access to all system memory. It has write access.

You can get ps to tell you the address of a running process. You can figure out where inside that running process the uid is stored. You can drop to OpenBoot and change that value. If you do that with, for example, a shell, you have nearly instantaneous root access.

Nifty. Much easier than shutting down the OS (usually hard) and booting off of a CD when you've screwed something up very badly.

Of course, that doesn't show how powerful it is outside the realm of being able to tweak your OS. But it implements a Forth interpreter and knows about most of the computer's hardware, third party stuff sometimes, but not always, excluded. It even implements TFTP and DHCP clients.