systemd is a suite of basic building blocks for a Linux system. It provides a system and service manager that runs as PID 1 and starts the rest of the system.
Cost / License
- Free
- Open Source (GPL-2.0)
Platforms
- Linux

nitro is described as 'Tiny but flexible init system and process supervisor' and is an app. There are more than 10 alternatives to nitro for a variety of platforms, including Linux, BSD, Mac, Self-Hosted and Python apps. The best nitro alternative is systemd, which is both free and Open Source. Other great apps like nitro are OpenRC, runit, Launchd and s6.
systemd is a suite of basic building blocks for a Linux system. It provides a system and service manager that runs as PID 1 and starts the rest of the system.

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...
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.
a free system array created by Apple inc. For BSD - including macOS as macOS is based on the Darwin kernel of BSD
s6 is a small suite of programs for UNIX, designed for process supervision. It can be used as an init system. You can also use all its programs separately.
Supervisor is a client/server system that allows its users to monitor and control a number of processes on UNIX-like operating systems.



Chaperone is a lightweight alternative to process environment managers like systemd or upstart. Chaperone provides an extensive feature set, including dependency-based startup, syslog logging, zombie harvesting, and job scheduling.
The Sysvinit package contains programs for controlling the startup, running, and shutdown of the system.
The nosh package is a suite of system-level utilities for initializing and running a BSD or Linux system, and for managing daemons.
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.

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...
hummingbird is an init system designed for speed. It does nothing more than start the system and stop the system by default. There are three main "runlevels", fs which is called directly after the pseudo filesystems necessary for the system to run have been mounted...