Jukebox is a collection of reusable components that allow you to create a flexible server-side and middleware framework. It features semaphores and services (not quite your usual set), a Finite State Machine implementation based on Generics, a Datastream framework (data producers, consumers and loggers), and a JDK 1.6 compliant JMX framework based on Annotations.
Hibersap is a small framework that offers an abstraction layer on top of the SAP Java Connector (JCo). It maps Java classes to SAP function modules using Java Annotations and reduces the technical code to call a function in a SAP back-end system. Hibersap’s API is very similar to Hibernate, thus offering a familiar programming interface to developers of enterprise applications.
metagloss is an annotation-centric Android library for reducing boilerplate code. Relying on run-time parsing and compile-time code generation, metagloss provides facilities for mapping XML and databases to data objects, dealing with preference screens and working with DB queries.
Contracts for Java (Cofoja) adds contract programming support to Java through simple yet powerful annotations: @Requires, @Ensures, @Invariant, and @ThrowEnsures. Contracts are inherited from interfaces and superclasses and can be enabled selectively during development then disabled for release.
Yap4j is the simplest library for parsing CSV files in Java. It deserializes CSV files into a list of POJOs using a set of Java annotations, while allowing you to specify Object-CSV mappings. It automatically converts to and from a wide range of data types, and includes support for types from popular libraries such as Joda Time, and support for custom record delimiters.
Immutables allows you to embrace immutablity to tackle complexity and concurrency challenges. To get the benefits of immutability in Java, there's an annotation processor to easily create simple and consistent value objects. You can think of it as Guava's Immutable Collections but for regular objects. It includes support for JSON marshaling, MongoDB repositories, and JAX-RS.