Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Zoho Desk - Industry's first context-aware Helpdesk Software
HelpNinja - Simple & Affordable help desk
Salesforce Service Cloud - Service Cloud integrates customer service with social networks and provides a self-service customer portal and knowledge base system.
SupportYourApp - Connecting talented people with the blooming IT industry to help them grow faster by outsourcing support.