Our engineering team tried alternatives to Zulip (Slack, Mattermost, and others) during the period when Zulip’s future was unclear and it was receiving very little support. We preferred Zulip enough to switch back to it even though the mobile apps were basically non-functional (they’re now supported again).
The “killer features” for me were:
- Topic-based threading, which allows multiple conversations to occur simultaneously without having to creat a new stream (Zulip’s equivalent to channels) every time. This also makes it easy for me to contribute to a conversation hours (or days) later and have everyone else understand what I’m talking about.
- Relatedly, he ability to mute topics I don’t care about but see everything else within the stream.
- An intelligent global view that makes following multiple conversations at once easy