Having used team chats based on Jabber, IRC, Slack (in that chronological order), there is a huge difference. Jabber and IRC have always been pure chats, whereas Slack is the first chat platform where people actually use integrations and bots to a large extent. (Also, Jabber/IRC doesn't have /remind, my personal killer feature about Slack.)
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It's called IRC/Jabber + whatever web/GUI/CLI UI is desired. Many companies deploy it internally.
Having used team chats based on Jabber, IRC, Slack (in that chronological order), there is a huge difference. Jabber and IRC have always been pure chats, whereas Slack is the first chat platform where people actually use integrations and bots to a large extent. (Also, Jabber/IRC doesn't have /remind, my personal killer feature about Slack.)