But the end goal is not sending messages, the end goal is getting the person who knows about the projector to see your message and respond, for you to see that response, etc.

In a moderately sized company, Slack is better than the WhatsApp solution, since you can direct the message at roughly the correct set of people, by spending the extra time to choose a channel. In turn, those people are more likely to get the message in time to act on it, because the message won't be buried under tons of messages meant for other people in the company.

Zulip takes that a step further, by adding subject lines to messages. The same tradeoff applies.

I think in the end the question really is how much more work it is to add the extra signal. The best case would be you could send messages like in WhatsApp (no subject line, and every message goes to the entire company), and read messages like in Zulip (subject lines, and with channels limiting audience). For both Zulip and Slack, the premise is that we can drive down the cost of adding the extra signal to low enough.

> you say "the medium correspondingly encourages more multi-line, thoughtful posts". Writing more thoughtful messages and coming up with subject lines by definition requires more time... how can it not?

I think the key here is that you can write more multi-line, thoughtful posts, and they come through and sustain a real conversation much better than they do on Slack or IRC. But when that's not what's called for, you can also write super-quick short messages too.

For example, a few months ago the Zulip developers gathered in one place for a week to hack together. We had a stream (~channel) for the event, and one frequent topic in it was "schedule". A lot of the messages there were like "@all dinner's ready" -- dashed off on a phone, notifying everyone in the group, so a lot like sending to a WhatsApp group.

But other messages on the same topic were things like the next day's schedule or some detailed logistics, sent from a laptop with a real keyboard. It was helpful to have those details in the same thread as context above the quick right-now updates.

Other topics contained a variety of side discussions, some consisting of quick short messages ("found an X, who lost it?"), others detailed and thoughtful. A lot of those would have been lost in the noise in a Slack channel or a WhatsApp group, or would have added noise to make the other conversations hard to follow, or both.

And it was extremely helpful that all of the above was in the same system that we use all the time for in-depth technical discussion and other collaboration.