Most (all?) of the Apple iOS apps and data can be collaboratively shared, edited, etc over iMessage and it is extremely seamless with fine-grained access controls. I get people sending me calendars, notes, slide decks, documents, etc to either read or work on together via iMessage/iCloud. You can selectively share most things in your iOS environment with any other person in the iOS ecosystem. Google Apps is a pale imitation of this. And the security is tight.

I’ve never seen anything like this on any other chat app I’ve used. Most objects in iOS can be directly shared or collaborated on over iMessage, and that is a very rich set of objects. People that only use iMessage don’t even realize other chat apps can’t do some of these things.