[1000100_1000101]

You don't need everyone to agree on an interface if you approach things slightly differently. Like Unix shell scripts and pipes, each program can have its own particular inputs and outputs, as long as they're useful and documented... people will find ways to stitch them together.

This was the approach taken by Arexx. I've never used or seen IBM's Rexx outside of the Amiga version, Arexx. While a PC version of Rexx existed, it's obvious why it didn't take off... IBM wanted exorbitant fees per end user, and even higher developer fees. As a result it had no users, and with no users, no software bothered to supported it. Most PC developers likely had no idea it was even a thing.

It was different on the Amiga. Commodore somehow got the rights to including it in their OS, no additional licensing required. As such, there was a ready user base, and thus many apps had Arexx support. You could query data from one app, massage it in the scripting language, then pass it off to another app.

It was a well-loved feature allowing all sorts of automation that wasn't really available anywhere else.

[bodhiandphysics]

you still need to agree on some things... For instance even if you're passing data through text, you have to agree on the actual encoding (Unix uses ascii, but there are lots of different text encodings!). You also have to agree on the meta-properties of the communication. How do programs find other programs to communicate with? How do they actually pass data to each other? How do they maintain transactional integrity (i.e. a request sometimes needs to be atomic, either happening or not happening, and the requesting program needs to know if a request happened!).