This was an interesting comparison: https://skarnet.org/software/s6/why.html

I've also found this useful: https://ahmet.im/blog/minimal-init-process-for-containers/

And this looks really good: https://wiki.gentoo.org/wiki/Comparison_of_init_systems

Runit seems way simpler. It's both good and bad. I like its minimalism, but it involves more imperative shell script style, less declarative. The documentation is very terse, too; I learned a lot from reading Void init scripts which I wish was reflected in the docs. (Maybe I should send a patch.)