MongoDB - MongoDB (from "humongous") is a scalable, high-performance NoSQL database.
Qizx - XML Databases
Redis - Redis is an open source in-memory data structure project implementing a distributed, in-memory key-value database with optional durability.
BaseX - BaseX is a very light-weight, high-performance and scalable XML Database engine and XPath/XQuery...
ArangoDB - A distributed open-source database with a flexible data model for documents, graphs, and key-values.
eXistdb - High-performance native XML database engine and all-in-one solution for application building.