My favourite is currently NixOS for a router, entire configuration (system packages, version, firewall rules, interfaces, VLANs, etc) is declarative and can be deployed with automatic rollbacks in the event of misconfiguration.
This is what I’m working on right now too, built around an APU board. I’m also wrestling with hostapd to get WiFi working as well, just because. Once it’s working I’ll try and write it up.
I also love this. I ran into issues trying to get it working with extra very strict kernel security features enabled, but even then I eventually figured it out. Was really nice to use.
That sounds very interesting. Have you documented it somewhere?