The XSD editor is a cross-platform XML editor. Although it can be used to edit any type of XML file, the editor is specifically designed to allow easy creation, editing, and validation of XML Schema (XSD) files.
This tool has been nearly indispensable. By leveraging Xerces, it performs a much more thorough validation than XMLSpy. The messages for validation errors are also much more useful. I inherited a bunch of XSD fragments, and with XSDEditor was able to turn that into a usable, fully validated, set of files. Thanks!