Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
GetChat.App - Add WhatsApp chat to your website for free
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.
Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
Avochato - Text messaging for your business.
Crisp Chat - Multi-channel customer support software