If you mean restricting filesystem access to random programs, I think that's already possible on macOS (with TCC) and Linux (with Flatpak), but the underlying m

If you mean restricting filesystem access to random programs, I think that's already possible on macOS (with TCC) and Linux (with Flatpak), but the underlying mechanisms aren't very robust and can be easily bypassed by malicious code. If you mean a true capability-based OS, there is Fuchsia, which doesn't seem to be used yet, and RedoxOS, which is in development.