Liquid XML Studio is a Freeware XML Schema Editor, and much more.

Simple enough for new users to pick up quickly and comprehensive enough for experienced users deal with the advanced features of the XSD standard.

Note: Their are 2 versions of Liquid XML Studio a Freeware and Professional edition.
Find out more about the differences.

Core Features

• Design and Build new XSD schemas graphically                           
• Edit or modify existing XSD schemas.
• Visualize an XSD schema making it simpler to understand and work with.
• XML Designer for building and validating XML to comply with your schema.
• Infer an XSD from XML sample documents.
• Generate XML Samples from an XML Schema.
• Call Web Methods.
• Visualize the results of XPath expressions
• Generate HTML documentation from your XML Schema (including hyper linked diagrams).
  

• Quickly Visualize, Create or Edit your XML Schema (XSD)
• Intuitive interface, while still offering access to the advanced XSD features
• Drag and drop, Copy and Paste, Undo/redo options
• Split screen - XSD source code and graphical view are both editable and in sync.
• XSD Validation
• Create Sample XML for your schema
• Intellisense on the XSD code view
• Context sensitive properties
• View and edit any schema component
• Expand and collapse the schema diagram
• Printing
  

• Syntax Highlighted XML Editor
• Intellisense
• Infer an XML Schema from one or more XML documents
• Auto Complete
• XML Validation
  • Well formed
  • Validation against XSD schema

• XPath Expression Builder, construct and visualize XPath expressions & search results.
• Web Service Browser, examine and call web methods.
• XSD -> HTML Doc, document your XML Schema. Generated HTML includes diagrams and annotations from your schema (See Samples).
• XML Formatter (Pretties up you XML)
• Find and Replace
• Versatile environment, windows are dockable/pinable/floatable
• Create Sample XML From your XSD
• Infer XSD From XML Samples