While reading this, the old ARexx (Amiga Rexx) popped into my head. It was a scripting language that in itself wasn't very noteworthy. However, it also made it easy for applications to expose functionality through an ARexx port. And again, offering up an API itself isn't noteworthy either. But it shipped by default in the system and if an application wanted to open itself up for scripting, ARexx was the natural choice. As a result, a ton of applications did have ARexx ports and there was a level of universality that was way ahead of its time.
Come to think of it - I don't know what the modern equivalent would be. AppleScript?
Come to think of it - I don't know what the modern equivalent would be. AppleScript?