HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
HelpNinja - Simple & Affordable help desk
SupportYourApp - Connecting talented people with the blooming IT industry to help them grow faster by outsourcing support.
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
TaskUs - Outsourced customer support (powers Uber & Hotel Tonight)