Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
AirHelp - Get paid when you're delayed!
GoSquared Live Chat - Beautiful, simple, and free live chat for your website
Service - Customer service issues solved for you, on demand, for free.
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.