SubEthaSMTP is an easy to understand Java library that provides a receptive SMTP server component. By plugging this component into your Java application, you can easily receive SMTP mail using a simple abstract Java interface. Also included is a small sub-project called Wiser, an easy to use incoming mail testing framework.
JCPP is a complete, compliant, standalone, pure Java implementation of the C preprocessor. It is intended to be of use to people writing C-style compilers in Java using tools like sablecc, antlr, JLex, CUP, and so forth. It has been used to successfully preprocess much of the source code of the GNU C library.
VRaptor 2 is a Web-based MVC and IOC framework based on many frameworks and ideas (Seam, Stripes, Webwork, Hibernate Annotations, etc). It makes full use of Java 5 Annotations. It favors convention over configuration, because configuration in XML/properties/annotations is always easy to make mistakes and repetitive (aka copy and paste in many places). This framework uses a more imperative approach, instead of having many XML files to configure lifecycle and other properties. Most of the settings go inside plain Java objects (POJO), so the team knows exactly what is going on and where.
Aranea is a hierarchical Model-View-Controller Web framework that provides a common, simple approach to building Web application components, reusing custom or general GUI logic, and extending the framework. The framework enforces programming using object oriented techniques with POJOs and provides a JSP tag library that facilitates the programming of Web GUIs without writing HTML. In addition to being a full-fledged Web framework in its own right, it provides a powerful and simple component system that allows the framework to be tailored by configuring the reusable modules and adding modules only for the missing features.
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.