Slack has finally added one of its most requested features: threads! Updated versions of Slack for all platforms and the Web now allow you to start a thread in reply to any message. Threads are shown in both a channel-specific sidebar in the Web and desktop apps, and in a pane in the mobile apps. You can also view threads in which you’re a participant in a new All Threads/New Threads view reachable from the sidebar. I wrote a TidBITS article explaining the feature and how best to use it.
At this writing, we have no plans to update this book. The addition of threading didn’t change other features in the ecosystem.