Slack is the one that clicked for me as well. I used it with some friends just to try it out. Then at work our small team used the free version, without anyone'

Slack is the one that clicked for me as well. I used it with some friends just to try it out. Then at work our small team used the free version, without anyone's permission, just to play around and see how we liked it. Turns out another team did the same thing and we decided to merge the workspaces. Then some upper level people got wind, saw it was going well, and soon after the entire 200 person company was on it. Not saying our team was responsible for the purchase, but it clearly helped Slack gain a foothold as "a tool we use".