For me, Slack's success was not just about the design, but also the performance. Slack showed up right about the time HipChat started having major outages. I was running an ops team and we were often unable to communicate because of broken HipChat. Slack showed up and it was lightning-quick and much more reliable. I pushed hard for my employer to adopt it company-wide and they did.<p>Things have changed a bit and Slack has definitely had some growing pains but I still love it. I took a new job at a company that uses HC for compliance reasons and I sorely miss Slack and dread the HC outages which still happen.