SerenityOS isn't a memory safe OS. That's for sure. No innovation here…

But anyway, there are not much safe OSes out there I guess.

There are all the Rust experiments (with usually a shitload of `unsafe` code in there).

There was the Midori experiment by MS (no clue whether there is source code available).

There have been Java based OSes.

But all in all, there doesn't seem to be anything that has got any traction.