JBoss ModeShape
JBoss ModeShape is a descendent of JBoss DNA, a JCR product. It is itself a JCR product with a slew of additional services and functionality.
From the ModeShape website:
ModeShape is a distributed, hierarchical, transactional, and consistent data store with support for queries, full-text search, events, versioning, references, and flexible and dynamic schemas. It is very fast, highly available, extremely scalable, and it is 100% open source and written in Java. Clients use the (JSR-283) standard Java API for content repositories (aka, JCR) or ModeShape's REST API, and can query content through JDBC and SQL.