The ASF is made up of nearly 100 top level projects that 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 IvyDE
Integrate Ivy in Eclipse with the IvyDE plugin.
IvyDE lets you manage your dependencies declared in an ivy.xml in your Java Eclipse projects. IvyDE will contribute to the classpath of your Java project, with the classpath container. It also bring an editor of ivy.xml files, with completion.
Apache Commons JXPath
XPath for Java Objects
A Java-based implementation of XPath 1.0 that, in addition to XML processing, can inspect/modify Java object graphs (the library's explicit purpose) and even mixed Java/XML structures.
Apache Derby
Apache Derby is an open source relational database implemented in Java.
Apache Derby is an open source relational database implemented entirely in Java. It has a small footprint that makes it easy to embed in any Java-based application, but it also supports the more familiar client/server mode. It is based on the Java, JDBC, and SQL standards, making code developed more portable to standards-compliant databases.