I have read "multi-agent system" or "agent based programming" a few times, but I have not yet understood what is meant by it.
https://theconversation.com/how-big-data-and-the-sims-are-he...
The featured simulation is by Nick Malleson. His website is full of excellent (and relavent) resources.
Smalltalk had some groundbreaking ideas -- but "an app. is an image of the whole, monkey-patched class hierarchy shipped with the entire system" certainly wasn't it's greatest contribution.