Slack is an app designed to act more like an instant messenger. It is available on desktop and devices (iOS, Android and Windows).
It seems like a great way for teams within a company to communicate with one another. You can upload a file and multiple people can comment on the same file. This is more difficult with email because the attachment might not be sent every time someone responds to the email. It can be a hassle to dig through old emails to find which one had the attachment. Slack seems like it would solve that problem by having the file available in the conversation.
I don’t think it will ever completely replace email at any point in the near future, but it is definitely something to look into.
See more about the app here: Slack