I think the macOS User Defaults system is still my favorite config system. Unified api (`defaults` and NSUserDefaults), but stored in user-editable (and easily cleaned up) files with standardized naming and formatting. It's not perfect (kooky and unwieldy XML syntax, no standard equivalent of conf.d), but it solves the pain points I've seen with the Windows Registry (monolithic inscrutable database) and unix commands (random config files each with their own custom place and format)
