Chatlio - When you have a business to run, your average instant messaging software just will not do. You need an internal presence upon which your entire team can collaborate on. Read more about Chatlio.
Trello for Slack - Organize anything with anyone, inside Slack
slalert! - Get notified in Slack when your company/keyword is mentioned
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Talkus - Chat with your website users from Slack
Halp - Slack-first ticketing for internal helpdesk