@sashin The most popular "out of the box" option with good documentation is OpenRC. runit is another popular option and is generally more stable. S6 is focused on speed but is probably the most difficult to configure. Apparently there's a more user friendly focused version of S6 called suite66 but I know very little about it.
If you want the nitty gritty details, Gentoo has a really great graph comparing the different init systems and how they function. https://wiki.gentoo.org/wiki/Comparison_of_init_systems