Zulip threads (topics) are fundamentally different from slack threads. TL;DR Slack threads are an after-thought add-on, Zulips topics are a first-class citizen

Zulip threads (topics) are fundamentally different from slack threads. TL;DR Slack threads are an after-thought add-on, Zulips topics are a first-class citizen. Slacks threads can branch of at any point from any message in a channel - if you miss the start of the thread message, it disappears unless someone cross-posts to the channel or mentions you. This is by far the biggest problem I have with slack threads. Zulip organizes into streams and topics, streams being roughly equivalent to channels and topics similar to threads. However, unlike slack, every message must live in a topic. Topics that have seen a message lately bubble to the top, topics that don't see activity fall to the bottom. You can still see the full stream in chronological order, but messages are grouped by and visibly marked with the topic they belong to. This makes it much easier to both follow a stream and still mentally follow multiple conversations in the same stream.