Reading your comment, it also came to my mind this inter-process communication from KDE called DCOP, which allowed you to call methods from KDE applications supporting DCOP from the command line or shell scripts. For example, the Konqueror web browser exposed functions to open tabs, navigate to URLs... instant messaging applications allowed you to query your contacts' online status, send a message, the music player would let you control the playlist, etc.
It then (IIRC 15 years ago) became deprecated in favor of DBUS, but I remember it was not as straightforward and simple to use as DCOP was, and also the applications, at least by the time, weren't supporting lots of useful operations with DBUS.
It then (IIRC 15 years ago) became deprecated in favor of DBUS, but I remember it was not as straightforward and simple to use as DCOP was, and also the applications, at least by the time, weren't supporting lots of useful operations with DBUS.