To clarify (since I can't edit), we use Slack as a replacement for email, and other apps for chat. It's great for sending quick code snippets. It's good for notifying the whole team when there's a new build for testing, as well as getting comments on that build. It's okay for bringing attention to a thing.

Notifications during office hours by default hurts it - instead of people not sending messages outside work hours, everyone just uses something else for notifications.

Dont forget dropbox was just shiny FTP :)