You can ping people to get their attention even if they are not online by @mentioning them. Depending on how the person has set their account up it can be by notifications via in-app sounds, visual alerts, and even email, SMS, or mobile app push notifications.
Instead of rooms or channels Zulip is built around topics. This allows you to have multiple conversations at the same time without conversations interfering with each another. It also allows you to reference conversations without clutter.
With Docker set up, you can install Mattermost with the following command: docker run --name mattermost-dev -d --publish 8065:80 mattermost/platform For other cases, installation instructions can be found here.