AntInstaller is a flexible front end for deploying applications using Ant build files as the engine. It provides a Swing GUI and a command line alternative for situations (such as server deployment) when X is not available. The installer is designed by creating an XML config file that describes the various pages of the installer and the input required from the user. The input is validated and can be dates, directories, options selected from a list, or other structured input. Once the properties are selected, AntInstaller runs and calls the selected targets. Primarily, it is designed for installing Java apps in a user-friendly way, but can be used for anything that requires structured input for Ant scripts.
Anteater is a testing framework designed around Ant, from the Apache Jakarta Project. It provides an easy way to write tests for checking the functionality of a Web application or of an XML Web service. It can test either HTTP requests or replies in various sophisticated ways. The ability to wait for incoming HTTP messages is unique to Anteater, which makes it especially useful when building tests for applications that use high level SOAP-based communication and asynchronous SOAP messages. Anteater provides XML and text logging support and the ability to render the logs into HTML reports.
Apache Byte Code Engineering Library (formerly known as JavaClass) is intended to give users a convenient utility to analyze, create, and manipulate (binary) Java class. Classes are represented by objects which contain all the symbolic information of the given class, in particular the methods, fields and byte code instructions. Such objects can be read from an existing file, be transformed by a program (e.g. a class loader at run-time), and can be dumped to a file. One interesting application is the creation of classes from scratch at run-time. Apache Byte Code Engineering Library (BCEL) may be also useful if you want to learn about the Java Virtual Machine (JVM) and the format of Java .class files.
Apache Cocoon is a Web development framework built around the concepts of separation of concerns and component-based Web development. Cocoon implements these concepts around the notion of "component pipelines", each component on the pipeline specializing on a particular operation. This makes it possible to use a Lego(tm)-like approach in building Web solutions, hooking together components into pipelines without any required programming.
The Apache JMeter is a 100% pure Java desktop application designed for performance and load testing of servers. It was primarily designed for Web/HTTP testing but it has been expanded to include support for a variety of testing modules. It ships with modules for HTTP and SQL databases (using JDBC). It may be used to test server performance both on static and dynamic resources, to simulate a heavy load on a server or network to test its strength, or to analyse overall performance under different load types. It also provides pluggable interfaces for customizing data visualization, test synchronization, and the construction and execution of tests.
Apache Jakarta Regexp is a 100% pure Java regular expression package. Expression syntax supports all of Perl5 syntax, with the exception of back reference substitution markers (several people have mentioned this lack, so please feel free to contribute a solution). It also supports a very limited subset of POSIX features. Performance and features are somewhat inferior to ORO, and the new JDK 1.4 (java.util.regex) package, but the package is especially small and features the ability to precompile expressions (without using object serialization) into byte arrays, thus avoiding the need to load the expression compiler.