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.
Types that extend and augment the Java Collections Framework.
Annotator components and a scalable integration and deployment framework for Unstructured Information analysis
The Apache UIMA project supports the community working on the analysis of unstructured information with a unifying Java and C++ framework, tooling, and analysis components, guided by the OASIS UIMA standard. It includes support for very large scaleout using networked clusters of compute nodes.
RESTFul web services based on JAX-RS specification
Apache Wink is a simple yet solid framework for building RESTful Web services. It is comprised of a Server module and a Client module for developing and consuming RESTful Web services.