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.
Apache Jackrabbit Content Repository
Apache Jackrabbit is a fully conforming implementation of the Content Repository for Java Technology API (JCR). A content repository is a hierarchical content store with support for structured and unstructured content, full text search, versioning, transactions, observation, and more. Typical applications that use content repositories include content management, document management, and records management systems.
Apache Buildr is a build system for Java-based applications, including support for Scala, Groovy and a growing number of JVM languages and tools.
We wanted something that's simple and intuitive to use, so we only need to tell it what to do, and it takes care of the rest. But also something we can easily extend for those one-off tasks, with a language that's a joy to use.
Apache log4php is a logging framework for PHP.