Threads as first class citizens is something that Zulip [0] focuses on, which makes it much easier to have multiple conversations within the same space. It also makes it easier to ignore any conversations you don't care about.

This avoids the problem with Slack where some people might use the threading features, while others ignore it. Personally I'm a huge fan of Zulip, having used HipChat, Slack, Mattermost, Skype for Business, and Discord in the past.

[0] http://zulip.org