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 Scout is an implementation of the JSR 93 (JAXR).
Apache Scout is an implementation of the JSR 93 (JAXR). It provides an implementation to access UDDI registries (particularly Apache jUDDI) in a standard way.
Java-based template engine
Velocity is a Java-based template engine. It permits anyone to use a simple yet powerful template language to reference objects defined in Java code. When Velocity is used for web development, Web designers can work in parallel with Java programmers to develop web sites according to the Model-View-Controller (MVC) model, meaning that web page designers can focus solely on creating a site that looks good, and programmers can focus solely on writing top-notch code. Velocity separates Java code from the web pages, making the web site more maintainable over its lifespan and providing a viable alternative to Java Server Pages...
Apache SpamAssassin is an email filter used to identify spam
Apache SpamAssassin is an extensible email filter which is used to identify spam. Using its rule base, it uses a wide range of advanced heuristic and statistical analysis tests on mail headers and body text to identify "spam", also known as unsolicited bulk email. Once identified, the mail can then be optionally tagged as spam for later filtering. It provides a command line tool to perform filtering, a client-server system to filter large volumes of mail, and Mail::SpamAssassin, a set of Perl modules.