Dynalist - Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.
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.
Workflowy - A better way to organize your mind.
XML Copy Editor - XML Copy Editor is a fast, free, validating XML editor.
Indigrid - Plain text outliner with side-by-side views.
Oxygen XML Editor - Oxygen XML Editor provides a comprehensive suite of XML authoring and development tools.