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.
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.
JRel is a library for the Java language that can be used to construct database queries in a programmatic fashion using a subset of the relational algebra. These queries are expressions in the form of 100% native Java code, and are translated at runtime into compliant ANSI-SQL usable with a variety of SQL databases.
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.
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.
The Geomajas API project contains some annotations that can be used to indicate which parts (which classes and which (public) methods or fields) are considered as the API. This is particularly useful for projects where you want to mark the API without the need to refactor everything to interfaces and factories.