avaamo - Simple, Secure Business Messaging
Drift - A messaging app that helps you grow your business.
SupportKit - Embed Zendesk support into your iOS app with 1 line of code
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Fleep for Business - Simple, open collaboration and chat with admin capabilities
Tars - TARS enables users to create chatbots that replaces regular old webforms.