Xmind - Xmind is a brainstorming and mind mapping application.
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
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
UserVoice - UserVoice integrates easy-to-use feedback, helpdesk, and knowledge base management tools in one platform that empowers users to speak and companies to understand.
Coggle - Coggle is a simple, beautiful, powerful way of structuring information.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.