Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Service - Customer service issues solved for you, on demand, for free.
Outbound Apps by Intercom - Embed apps right inside your messages
Intercom App Store - Integrate with Intercom and grow your business
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
indemandly - Live chat 2.0: Customer messaging that converts