Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Zirtual - Virtual assistants for busy people.
Raiseaticket - Raiseaticket is a 100% free cloud based helpdesk for customer service and support. The saas provides portal, workflows, insights to manage communications for the support and service process.
WoodBows - WoodBows provides Dedicated Virtual Assistants based in the USA, Philippines, and India at an affordable price.
Best Support System - Best Support System is self-hosted support ticket application.It handle support ticket, manage email ticket, collect any payment by paypal.
Prialto - Prialto employs expert virtual assistants that can efficiently assist you with challenging tasks.