Oh wow, you hit on a major topic in my book [1]. The Altos were all networked, via 3 MB Ethernet. MazeWar was a networked game (or "MMOG" in modern parlance) and it's on the cover of the book. In the book they spend quite a bit of time talking (and trashing, for some old school folks) how Ethernet worked.

I actually don't remember any live chat apps, but that doesn't mean there weren't any; there probably were. We relied on email mostly.

[1] https://www.albertcory.io