HelpSpace - The team inbox with super powers
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Awesome Support - Awesome Support is the most versatile and feature-rich help-desk plugin for WordPress.
ChatinBox - A conversational user engagement platform for your users
Drift - A messaging app that helps you grow your business.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.