I haven't yet tried Zulip's threading model, but I can certainly say I'm not pleased with Slack's. It can be very frustrating to try and trace a conversation b

I haven't yet tried Zulip's threading model, but I can certainly say I'm not pleased with Slack's. It can be very frustrating to try and trace a conversation backwards in a crowded Slack channel. I haven't used IRC in a while, but at least my client had a feature to toggle highlighting on a back-and-forth conversation, but that wasn't perfect.