The ASF is made up of over 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 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 Roller is a full-featured, multi-user and group blog server suitable for blog sites large and small.
Apache Roller is a full-featured, multi-user and group-blog server suitable for blog sites large and small. It runs as a Java web application that should be able to run on most any Java EE server and relational database. Roller's installation guide covers deployment on Tomcat, GlassFish, and JBoss application servers using a MySQL, Derby, or PostgreSQL database. Users however have reported success running Roller on other app servers and databases. - Multi-user blogging: can support tens of thousands of users and blogs - Group blogging with three permisson levels (editor, author and limited) - Support for comment moderation and comment...
Tools and infrastructure for the template engine
VelocityTools is a collection of Velocity subprojects with a common goal of creating tools and infrastructure for building both web and non-web applications using the Velocity template engine.