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

Launchd is described as 'A free system array created by Apple inc. For BSD - including macOS as macOS is based on the Darwin kernel of BSD' and is an app. There are more than 10 alternatives to Launchd for a variety of platforms, including Linux, BSD, FreeBSD, OpenWrt and Docker apps. The best Launchd alternative is systemd, which is both free and Open Source. Other great apps like Launchd are OpenRC, runit, s6 and sysvinit.
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.
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.
The Sysvinit package contains programs for controlling the startup, running, and shutdown of the system.
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...