KataOS was published by google on github recently
It is based on seL4 microkernel, it uses musl ported to seL4 runtime environment. Seems to be supporting arm/aarch64/x86/riscv ports right now.
Its implemented in rust almost entirely, I guess a good start for a security focussed software.
It will be interesting to see when CAmkES framework is made available in due course, since that will help in assessing the userspace capabilities when it comes to 3rd party apps.
To prove-out a secure ambient system in its entirety, we’re also building a reference implementation for KataOS called Sparrow, which combines KataOS with a secured hardware platform. So in addition to the logically-secure operating system kernel, Sparrow includes a logically-secure root of trust built with OpenTitan on a RISC-V architecture. However, for our initial release, we’re targeting a more standard 64-bit ARM platform running in simulation with QEMU.
hopefully it will be of some consequence and get some traction in OSS ecosystem 
