The ASF is made up of nearly 150 top level projects which cover a wide range of technologies. Chances are if you are looking for a rewarding experience in Open Source, you are going to find it here.
Apache Whisker assists assembled applications to maintain correct legal documentation.
Apache Whisker allows an application to models the licensing characteristics of the contents of its distributions. Use cases are auditing the model against the contents of a distribution, reporting on the contents of a distribution and generation licensing documents (LICENSE, NOTICE and so on) for a distribution. Whisker distributes tooling for the command line and build system such as Maven.
Java libraries for bare-bone HTTP communication, including support for NIO.
HttpCore is a set of low level HTTP transport components that can be used to build custom client and server side HTTP services with a minimal footprint. HttpCore supports two I/O models: blocking I/O model based on the classic Java I/O and non-blocking, event driven I/O model based on Java NIO. The blocking I/O model may be more appropriate for data intensive, low latency scenarios, whereas the non-blocking model may be more appropriate for high latency scenarios where raw data throughput is less important than the ability to handle thousands of simultaneous HTTP connections in a resource efficient manner....
Rule based XML->Java object mapping module
The Digester package lets you configure an XML->Java object mapping module which triggers certain actions called rules whenever a particular pattern of nested XML elements is recognized.