Yeah, instead of using the database you can use environment variables. You have to manage auditory, rollbacks and all that jazz on your own, of course.

We once had a project that used Zookeeper for that, too.

And finally I’ve got to mention that if you build your systems with Erlang or Elixir and you configure your apps using application environment instead of System Settings, you can use WombatOAM to manage your configuration in very System-Settings-y way.