Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
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.
Aircall's Zendesk App - The best phone companion for Zendesk
Avochato - Text messaging for your business.
Drift for Slack - Talk to your website visitors & customers in real-time
Crisp Chat - Multi-channel customer support software