systemE is described as 'Using the tooling in this repo, I am able to boot from linux to sinit as PID1, and from there to Emacs acting as PID2 using --script mode, performing all typical rc.boot system initialization using Emacs lisp until we hit the getty'. There are more than 10 alternatives to systemE for a variety of platforms, including Linux, BSD, Mac, Self-Hosted solutions and Python. The best alternative is systemd, which is both free and Open Source. Other great apps like systemE are sysvinit (Free, Open Source), OpenRC (Free, Open Source), runit (Free, Open Source) and nosh (Free).
systemd is a replacement for the init daemon for Linux (either System V or BSD-style). It is intended to provide a better framework for expressing services' dependencies, allow more work to be done concurrently at system startup, and to reduce shell overhead.
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.
Finit is a small SysV init replacement with process supervision similar to that of daemontools and runit. Its focus is on small and embedded GNU/Linux systems, although fully functional on standard server and desktop installations.
eudev is a fork of systemd with the aim of isolating udev from any particular flavor of system initialization. This is a project started by Gentoo developers to ensure udev remains system initialization and distribution neutral.
procd is a process and system init service for OpenWRT. It's less resource intensive as it's intended for embedded devices, works with busybox and uClib, hotplug2, libubox and ubus. It watches configuration files to start or restart services and init scripts