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

HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.

UseResponse - Open-source, self-hosted customer feedback software, live chat and helpdesk system that you can install on your server. Organize documentation using knowledge base and get feedback from social networks with centralized system

Dr.Explain - Dr.Explain software is a help file authoring tool.

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

MadCap Flare - Documentation for Any Audience, Language or Format