There's also Cyclone which tried to be safer than C in some respects. It was used by a DoD Linux distro called AUXillery OS iirc. Mysteriously disappeared from the internet a few years back. They were making sure every bit of the kernel was safe. I think its goals was for jet planes or something mission critical enough. Kept looking back every few years on Wikipedia till the page disappeared and the homepage.

Edit: Wow now I absolutely cannot find a darn thing about that distro. Used to be one last page detailing the project left. It was quite interesting, wish they hadn't shut down the homepage at least.

Edit 2: Looks like it was called AuroraUX here's a bit more info on it:

https://www.openhub.net/p/AuroraUX https://www.phoronix.com/scan.php?page=news_item&px=MTIyMTI

Even found a blog post from someone who was apparently developing AuroraUX:

http://ultravioletos.blogspot.com/2009/09/opensolaris-distro...

Gotta love mysterious little Operating Systems. Looks like they were being maintained by Blastwave which was some sort of OpenSolaris focused company.

Found a Spanish wikipedia entry still alive which mentions support for Cyclone:

https://es.wikipedia.org/wiki/AuroraUX

(Google Translate if you don't know Spanish :)