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
Dr.Explain - Dr.Explain software is a help file authoring tool.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Enchant - The easiest way to scale personalized customer support
HelpSmith - HelpSmith is a help authoring tool to create CHM HTML help files, manuals, and PDF documents.