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.
The Apache Accumulo sorted, distributed key/value store is based on Google's BigTable design. It is built on top of Apache Hadoop, Zookeeper, and Thrift. It features a few novel improvements on the BigTable design in the form of cell-level access labels and a server-side programming mechanism that can modify key/value pairs at various points in the data management process.
Apache Axis2 is a service hosting and consumption framework that makes it easy to use SOAP and Web Services
Apache Axis2 is a toolkit for creating and using Web Services, including SOAP, MTOM, XML/HTTP and advanced WS-* standards such as WSRM and WSSecurity. Axis2 includes a very fast runtime engine, together with tooling support for WSDL and WS-Policy, and plugin support for WS-Addressing, WS-ReliableMessaging, WS-Security, WS-Eventing, WS-Transactions, WS-Trust and WS-SecureConversation. Axis2 runs either standalone or hosted in Tomcat or other servlet containers.
Aggregated multi-channel documentation framework, separation of concerns.
Apache Forrest™ software is a publishing framework that transforms input from various sources into a unified presentation in one or more output formats. The modular and extensible plug-in architecture of Apache Forrest is based on Apache Cocoon and the relevant industry standards that separate presentation from content. Forrest can generate static documents, or be used as a dynamic server, or be deployed by its automated facility.