Their site says:

- Every line of code in the firmware, including building an operating system from the ground up with device drivers and IP stack.

- The FireBrick's hardware platform is not used in any other devices and the FireBrick's codebase / firmware is not used in any other hardware.

Given the feature set I'm a little dubious that it's all in-house. There are a ton of man-years of code in there.

It would be interesting to know the history of the software.

This blog post has a few hints [1]. Apparently they had to rewrite a load of code when they moved to a multicore processor, so it definitely seems to be in-house software.

[1]: https://www.firebrick.co.uk/about/news/version-20/

Thanks for that link.

It's absolutely wild to think about a suite of software this sophisticated that exists outside the realm of Unix, Windows, or any of the long-term players in the embedded networking device market. I know there are boutique embedded IP stacks out there but it still boggles my mind that a small company like this has had sufficient revenue to keep up with the "churn" in the networking space for 20+ years w/o leaning on free/open-source software.

Piling-on to my own comment: Searching the site https://www.revk.uk for the keyword "firebrick" returns a ton of results detailing the development. It looks like it's exactly what it says on the tin-- a proprietary operating system with its own implementations of a ton of protocols.

I wish I had a reason to interview RevK about the Firebrick code. I think it would be an immensely interesting topic.