MarkLogic - Schema-agnostic Enterprise NoSQL database technology, coupled w/ powerful search & flexible application services
XML Copy Editor - XML Copy Editor is a fast, free, validating XML editor.
BaseX - BaseX is a very light-weight, high-performance and scalable XML Database engine and XPath/XQuery...
Oxygen XML Editor - Oxygen XML Editor provides a comprehensive suite of XML authoring and development tools.
Apache Xerces - Advanced XML parser, including support for XML Schema, DOM Level 2, and SAX.
Liquid Studio - XML Tools Provider: XML Studio - Graphical XML Schema Editor.