Weaving Threads (Slack Several People Are Coding blog)

Check the full post for an overview Slack's conversation threading model; also see Threaded messaging comes to Slack (Slack Several People Are Typing blog)

"If you use Slack to work with your team, you might notice a new feature — Threads. You can use Threads to reply to messages, organize discussions, and manage the many conversations that happen in Slack. As one of our most requested features, Threads has been in development for some time, and I wanted to share a little bit about our design process and what we learned."

Weaving Threads