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.
Liquid Studio - XML Tools Provider: XML Studio - Graphical XML Schema Editor.