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.
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.
Apache Traffic Server is an HTTP proxy cache.
Apache Traffic Server is fast, scalable and extensible HTTP/1.1 compliant caching proxy server. ATS can be used as a reverse, forward or even transparent HTTP proxy.
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.