Altova XMLSpy - The XMLSpy XML Editor is a powerful tool for editing XML and related technologies. It is the only XML Editor with patented SmartFix validation, enterprise-grade editors, converters, debuggers, and code generators.
Xmind - Xmind is a brainstorming and mind mapping application.
XML Copy Editor - XML Copy Editor is a fast, free, validating XML editor.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
Oxygen XML Editor - Oxygen XML Editor provides a comprehensive suite of XML authoring and development tools.
Coggle - Coggle is a simple, beautiful, powerful way of structuring information.