Xmind - Xmind is a brainstorming and mind mapping application.
Dr.Explain - Dr.Explain software is a help file authoring tool.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
Document360 - Self-service knowledge base software focused on SaaS Products & Enterprise Software Projects.
Coggle - Coggle is a simple, beautiful, powerful way of structuring information.
WinCHM - Creating CHM file, Make CHM file, Web Help. WinCHM Pro - Help authoring software (CHM, WebHelp, DOC, PDF) . With this powerful tool you can not only create chm file from scratch, but also convert a set of existing HTML files to a chm file.