Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Dr.Explain - Dr.Explain software is a help file authoring tool.
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
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.
Salesforce Service Cloud - Service Cloud integrates customer service with social networks and provides a self-service customer portal and knowledge base system.
MadCap Flare - Documentation for Any Audience, Language or Format