DataNucleus AccessPlatform is a standards-compliant Java persistence product. It is fully compliant with the JDO1, JDO2, JDO2.1, JDO2.2, JDO3, JPA1, JPA2 and JPA2.1 Java standards, and provides a REST API. It complies with the OGC Simple Feature Spec for persistence of geospatial Java types. It allows access to all popular RDBMS available today, together with the MongoDB, LDAP, NeoDatis, JSON, Excel/ODF spreadsheets, XML, BigTable, HBase, and Neo4j databases.
With MetaModel, you use a type-safe SQL-like API for querying any datastore. It is a data access framework providing a common interface for exploration and querying of different types of datastores. It isn't a data mapping framework. Instead, it emphasizes abstraction of metadata and the ability to add data sources at runtime, making MetaModel great for generic data processing applications, but less so for applications modeled around a particular domain.
The Apache ODF Toolkit is a set of Java modules that allow programmatic creation, scanning, and manipulation of Open Document Format (ISO/IEC 26300 == ODF) documents. Unlike other approaches that rely on runtime manipulation of heavy-weight editors via an automation interface, the ODF Toolkit is lightweight and ideal for server use.
Mr. Persister aims at providing a simple yet complete relational persistence API. Current features include easier JDBC operations via JDBC templates (Spring style), automatic connection/transaction handling, object relational mapping, dynamic report support, connection pooling, and more. Planned features include replication, JDBC driver debugging, more advanced ORM, and more.
Native XmlDB Query Daemon is a client-server version of the Sleepycat native XML database deployed as an Apache module. The client is a pure Java API, supporting XQuery, XPath, and an Xml:DB API layer. It comes with a graphical admin console. Server binaries are provided for Linux x86 and x86-AMD64; for other platforms, compile from source.
Resty is a small, convenient API to talk to RESTful services from Java. Its focus is on simplicity and ease-of-use, often requiring only two lines of code to access RESTful Web services. It lets you use much less code than URLConnection, it's simpler than Apache HTTP client, and it's more reliable than Jersey client.