The ASF is made up of more than 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.
The Apache PDFBox library is an open source Java tool for working with PDF documents.
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.
Apache River software provides a standards-compilani JINI service.
Apache River software provides a JINI service, which is a service oriented architecture that defines a programming model which both exploits and extends Java technology to enable the construction of secure, distributed systems consisting of federations of services and clients. Jini technology can be used to build adaptive network systems that are scalable, evolvable and flexible as typically required in dynamic computing environments.