Gentoo Wiki - OpenRC. OpenRC is a dependency based init system that works with the system provided init program, normally /sbin/init. It is not a replacement for /sbin/init. OpenRC is 100% compatible with Gentoo init scripts, which means you can probably find one for the daemons you want to start in the Gentoo Portage Tree. OpenRC, however, is not exclusively used by Gentoo Linux, so our goal is to be platform-agnostic.

runit is a cross-platform Unix init scheme with service supervision, a replacement for sysvinit, and other init schemes. It runs on GNU/Linux, *BSD, MacOSX, Solaris, and can easily be adapted to other Unix operating systems.

systembsd GitHub - jasperla/openbsd-wip - systembsd re-implementing specific systemd functionality for *BSD systems.

The nosh package is a suite of system-level utilities for initializing and running a BSD or Linux system, for managing daemons, for managing terminals, and for managing logging.