None with a GUI. I never released mine, and it's so far behind the times now it would take major work to get it ported to the 64 bit era and even then it would still be a C based OS.

This would be one way in which the Rust crowd could really make a difference.

Redox seems like a big effort that has at least some of the properties you're looking for:

https://www.redox-os.org/

But Redox is not a real time OS is it? I've not seen it written as part of the design or as a future goal.

It's a microkernel with even the drivers running in userspace, and has its own graphics stack. Seems the ideal setting to go for realtime requirements for the UI. I don't know if they've done anything in that direction but it seems the most well positioned to fulfill the requirements jacquesm was hoping for.

If they can see it through then that's a pretty good development. But there is more to QnX than just 'realtime' and 'microkernel', their whole philosophy about how a cluster of machines should work, the services location and so on is very well thought out. I'd be happier if Redox took some more lessons from Erlang and QnX on board than to do a re-invention. We have a lot of knowledge about systems like that lying around and re-inventing the wheel is fun but also ultimately will lead to having to re-learn those lessons the hard way.

Perhaps you should lend a hand then? :)

Not for large systems, but in the embedded space there is Nuttx (now managed by Apache foundation).