Immortal: A *Nix cross-platform supervisor (immortal.run)

It isn't clear to me what this does.

Does it replace systemctl? Or is it kind of a tmux alternative for background jobs?

Just reading the about, it looks cool. It uses runit and daemontools. I used void for a while, and I really liked runit. Personally, I don't like systemd. I don't want a debate, it's just my personal preference/opinion. I don't know daemontools that well, but it sounds like an interesting project.