NixOS, Guix System, SerpentOS, Bedrock and T2 Linux? Meta-distributions (could be either simple config-based reproducible systems, immutable atomic distros or functional transitive-dependency package managers), micro-kernels and distributed systems are the next cool, bleeding-edge stuff in FLOSS OSes, and most of those projects are still in development.
By the way, NixOS and Guix System use Stores, instead of FHS (File Hierarchy Standard). To take it up one notch, Guix uses shepherd instead of systemd, so if anyone over here dislikes Lenning or systemd for some irrational reasons, you've got a nice distro, I guess. But do note that you don't get to swap init systems in both NixOS and Guix System - you're stuck with systemd and shepherd respectively.