Beyond process supervisors

I was a fan of daemontools 20 years ago:

http://cr.yp.to/daemontools.html

If Bell Labs isn't Unix enough for you, you have to try Dan Bernstein -- daemontools agrees with systemd about what most of the problem is, but it stops at the minimum viable product.

Note that many web servers, database servers, and similar products have a root process which is basically a process supervisor -- it is a general resilience mechanism.