Zendesk - Zendesk is a beautiful, lightweight help-desk solution.

HiOperator - HiOperator is a virtual assistant that answers phone calls, chats with customers, provides in-app help, takes orders, and provides support.

Froged - One click solution providing easy-to-use marketing, sales and support services to turn website visitors into happy customers.

Service - Customer service issues solved for you, on demand, for free.

Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.

HelpStack - Open Source mobile help framework to support iOS and Android app users.