BaseX is a light-weight, high-performance, and scalable XML database system and XPath/XQuery processor, including full support for the W3C Update and Full Text extensions. An interactive and user-friendly GUI frontend gives you great insight into large XML data instances. It is platform independent and works out of the box.
Matreshka is a framework for developing information systems in Ada. It includes support for unbounded form strings of Unicode characters, including case conversions and folding, normalization, collation, support for regular expression matching, an XML processor, and a FastCGI module. It also provides capabilities to manipulate by UML models, which allows you to develop tools like code generators.