Uber did use HipChat instead of Slack, but mostly because Slack was uninterested in standing up servers for Uber. My understanding is that Slack basically ran a

Uber did use HipChat instead of Slack, but mostly because Slack was uninterested in standing up servers for Uber. My understanding is that Slack basically ran a single server instance for each Slack team. Atlassian bent over backwards for Uber, but just enough to make it functional. It was incredibly bad. Notifications would sometimes never arrive, or arrive hours delayed. Chats would take minutes to load. Messages would sit, spinning, waiting to be sent. It was like using 2G on your phone. Uber eventually replaced it with a (forked) Mattermost cluster.