EDIT: Thank you all for detailing your experience with, and hatred for, this miserable product. Your display of solidarity is inspiring. Now, say it with me:
The only thing it does better than Slack: A list of all my chats, most recent at the top, without any disappearing or grouped in some weird way. Slack annoys me.
I got slack for my college course, I left the group. I have no fucking idea what is going on on that app it was insanity. Seemed like 12 different groups of the same people and sometimes you got notifications sometimes you did not.