nosh is a multi-purpose init and process supervision software package made by Jonathan de Boyne Pollard. nosh is not presently supported in Gentoo.
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.
The flexibility of nosh allows it to be ran alongside with systemd as an service manager at least.
nosh also includes 'convert-systemd-units' to convert systemd unit files to nosh format.
https://jdebp.eu/Softwares/nosh/source-package.html - nosh source tarballs.