SchemaAgent 

Altova SchemaAgent 2006 is the new paradigm for modeling and managing advanced schemas and their components in workgroups. Visualize schema relationships and construct complex schemas from distributed schema elements via its graphical design view.
xml xml schema schema manager complex schemas manage schemas schema repository schema relationships

XMLSpy Professional Edition 

Altova XMLSpy 2006 Professional Edition is the industry leading XML development environment, providing intuitive editing views and powerful XML utilities to model, edit, transform, and debug XML technologies quickly and easily.
xml xml editor xml software schema editor dtd editor xsl editor xsl transformation xsd editor schema xml schema dtd xsl xslt xslt 2.0