From what I remember its a hardened BSD.
Anyhow you only get a serial command line which is Codian/Tandberg/Cisco based.
You do not get any additional operating system access.
So just see it as a locked down appliance.
Why do you need to know it?
Btw, you seem to have opened two messages, if you could close the other one.
Also please remember to rate helpful responses and identify helpful or correct answers.