I've spent a lot of time thinking about all the possible solutions to the problems associated with chat rooms. The issue that it's hard to talk about multiple things at the same time in a channel is common to Slack, IRC, Jabber, and just about everything else. So have spent a long time designing and building a better solution to those problems.
It's hard to talk about Slack's threading solution without also talking about what I think is the best way to solve that problem.
Zulip is great. After using it for a while, I no longer want to use anything else.
The light-weight topics make a lot of sense. You can quickly discuss a topic and then forget about it.
With Slack, you'll need to create a new channel, invite people into it, it's just much more overhead so you end up discussing in the main channel.
A huge issue with Slack, for me, is catching up with busy channels. You have to read all of it since you miss discussions on topics you're interested in. Zulip has a great solution to this issue.
I'm also impressed with how high-quality it is. They even have Nagios checks and everything. It has many features you miss in other products like Rocket Chat (full text search. administrative tools, ...).
I found it tasteful and relevant and didn't feel spammy because of the discussion contrasting a feature many people want that Slack doesn't have (or didn't until today and may not still be exactly what we want).
It's hard to talk about Slack's threading solution without also talking about what I think is the best way to solve that problem.