The only config system I've worked on that ever felt even vaguely satisfying was built around the excellent Typesafe (now Lightbend) HOCON implementation. The

The only config system I've worked on that ever felt even vaguely satisfying was built around the excellent Typesafe (now Lightbend) HOCON implementation. The fact that HOCON is a superset of both JSON and properties formats made adoption in a large org feasible since it could "just work" with the many already existing config files in those formats. While generalized programmability has obvious dangers, HOCON's ability to do variable substitution was super useful for the large amounts of config that was supposed to follow a convention, e.g. hostnames based on a template like ${service}.${env}.example.com