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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.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
XML Copy Editor - XML Copy Editor is a fast, free, validating XML editor.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.
Oxygen XML Editor - Oxygen XML Editor provides a comprehensive suite of XML authoring and development tools.