The Rust developers largely use Zulip as an IRC replacement, and I find its UI to be excellent for my use cases: keeping up with advances to conversations that happened while I wasn't present, fully ignoring conversations that I'm not interested in, and focusing on individual conversations that are happening in parallel. An extremely good experience for such a thoroughly-distributed operation. The only downside is the slight friction for extremely minor conversation; it's good to have side channels just for idle, non-topical chitchat, which isn't a great fit for the Zulip UI.
But you cannot get notified about a specific Zulip topic, can you? *That* blocks me to try to switch to it.