Free XML Formatting tool [closed]

I believe that Notepad++ has this feature.

Edit (for newer versions)
Install the “XML Tools” plugin (Menu Plugins, Plugin Manager)
Then run: Menu Plugins, Xml Tools, Pretty Print (XML only – with line breaks)

Original answer (for older versions of Notepad++)

Notepad++ menu: TextFX -> HTML Tidy -> Tidy: Reindent XML

This feature however wraps XMLs and that makes it look ‘unclean’.
To have no wrap,

• open C:\Program Files\Notepad++\plugins\Config\tidy\TIDYCFG.INI,
• find the entry [Tidy: Reindent XML] and add wrap:0 so that it looks like this:

[Tidy: Reindent XML] 
input-xml: yes 
indent:yes 
wrap:0