s6 is a small suite of programs for UNIX, designed to allow process
supervision (a.k.a service supervision), in the line of daemontools and
runit, as well as various operations on processes and daemons. It is meant
to be a toolbox for low-level process and service administration, providing
different sets of independent tools that can be used within or without the
framework, and that can be assembled together to achieve powerful
functionality with a very small amount of code.

Homepage:
https://skarnet.org/software/s6/
