Doxygen - Generate documentation from source code
Airim - Show personalised FAQs before live chat
Slate API Docs Generator - Create beautiful, intelligent, responsive API documentation.
HelpSite - HelpSite is a simple service to help your setup the perfect support centre or help site.
FastHelp - FastHelp is a Windows Help File Generator that produces online and offline documentation.
Manula - Manula is an online software for creating user manuals.