eXistdb
eXist-db is an open-source XML database and XQuery application server. It provides a native XML storage engine and a powerful XQuery processor designed to store, query, and manage XML documents. The system uses a document-oriented model with collections and resources and supports standard XML technologies such as XPath, XQuery, and XSLT.
Access and interfaces: It exposes HTTP-based interfaces including a REST API, WebDAV for file-like access, and
Querying and indexing: The platform supports XQuery as the primary query language, including the XQuery Update
Architecture and usage: eXist-db runs on the Java Virtual Machine, making it cross-platform. It can run as
License and availability: The project is open-source and released under the GNU Affero General Public License