I think plenty of people knows Slack has threads. Threads in Slack are secondary and are mostly meant for having conversations that people don't care about. Zulip has a much superior threading model. Each and every conversation is a new thread and has a topic. This model makes it extremely easier to catch up and participate in conversations. Once you get used to the threading model of Zulip its hard to tolerate threading model like Slack which is really inefficient and time wasting.

> Once you get used to the threading model of Zulip its hard to tolerate threading model like Slack which is really inefficient and time wasting.

This!

I got a bunch of our community to try out many of the different chat systems out there. Zulip was an interesting one as there were two points that really changed their perception of it as a platform:

1. When they were told there was a "Night Mode" - aesthetics are important! (something Slack arguably got right, IMHO beyond that it's just fancy IRC).

2. After around 5-10 minutes of playing around the penny drops as to why the stream and topic "zooming" is implemented in the way is it. Usually a "Holy Cow" moment.

Once you "get" it, going back to anything else feels like going back in time.

IME, it is awkward to revisit collapsed threads in Slack; especially after the thread has aged a few hours.

This is exactly the issue with the style of threads used in Slack, Teams, Hangouts Chat etc. Their useful half-life tends to them being forgotten quickly.

Topics aren't mandatory in Zulip. You can enable the "no topic" thread which makes them effectively optional.

Yes Slack has threads, but they aren't implemented in a way that's conducive to ad-hoc interaction over longer periods of time.