I think it is a _little bit_ off to just consider Slack to be a chat app. Sure chat is the core function...One thing I find super valuable about Slack is that it is a searchable archive. When a new person joins a company, they have literally years and years worth of searchable content. This helps get up to speed, cuts down on time spent asking questions etc. I find myself searching Slack many times a day pretty much every day at work. Not to mention automated workflows, calendar, drive integration etc.