Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Helpware - Amazing Customer Experiences. Together.
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
DeskMoz - DeskMoz Provides 24x7 Live Chat Agents for Your Website.
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
HelpSquad - Highly Vetted, Highly Trained chat support and conversion specialists