Beyond Compare - Beyond Compare allows you to compare files and folders.
XML Copy Editor - XML Copy Editor is a fast, free, validating XML editor.
WinMerge - WinMerge is an open source differencing and merging tool for Windows.
Oxygen XML Editor - Oxygen XML Editor provides a comprehensive suite of XML authoring and development tools.
Meld - What is Meld? Meld is a visual diff and merge tool targeted at developers.
Liquid Studio - XML Tools Provider: XML Studio - Graphical XML Schema Editor.