Base-X

Base'X "is a native, open-source XML database and efficient XPath/XQuery processor, including support for the latest Full Text and Update Recommendations. It supports very large XML instances and offers a highly interactive frontend. Base'X is written in Java and freely available for download. It is developed by the Database and Information Systems Group at the University of Konstanz." (from the web page)

The project page is located at http://base x.org/ (you have to copy the address manually because the spam filter won't let us save the complete link).