Zulip requires all conversations to happen inside of topics; think of it like an extremely lightweight and synchronous email, where the topic is the subject line. You can view a channel to see all its messages chronologically, and in the sidebar you can narrow to a single topic.
Zulip is great, I highly recommend it. On projects where I have to use Slack or Slack clones, I end up closing them when it's time to get work done because they're terrible at being productive and hopeless at preserving information for more than a few seconds. With Zulip I have successfully searched for information sent months ago/thousands of messages ago and still found it, thanks to the powerful search and mandatory topics.
Zulip is great, I highly recommend it. On projects where I have to use Slack or Slack clones, I end up closing them when it's time to get work done because they're terrible at being productive and hopeless at preserving information for more than a few seconds. With Zulip I have successfully searched for information sent months ago/thousands of messages ago and still found it, thanks to the powerful search and mandatory topics.