It is better than E-mail for instant and group communication, it is better in everything except audio/video calling that Skype. SMS and phone calls are not even

It is better than E-mail for instant and group communication, it is better in everything except audio/video calling that Skype. SMS and phone calls are not even in the same ballpark in terms of solving group communication problems. Disregarding the technical side of things, Slack is a great tool and it is quite understandable why it stuck: people like it.