eXist is an open source database management system built on XML (extensible markup language) technology. eXist stores information (data or metadata) encoded in XML. The database is queried using XQuery (XML query language), and follows many other W3C XML standards, including XPath and XSLT.
eXist includes a query editor and debugger. There is a large library of example data, code and applications that can be adapted.
Metacat is a flexible, open source metadata catalog and data repository that targets scientific data, particularly from ecology and environmental science. Metacat accepts XML as a common syntax for representing the large number of metadata content standards that are relevant to ecology and other sciences. Thus, Metacat is a generic XML database that allows storage, query, and retrieval of arbitrary XML documents without prior knowledge of the XML schema.
Morpho a program that can be used to enter metadata, which are then stored in a file that conforms to the Ecological Metadata Language (EML) specification. Information about people, sites, research methods, and data attributes are among the metadata collected. Data can be stored with the metadata in the same file.