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 ACE is a distribution framework that allows you to centrally manage and distribute software components, configuration data and other artifacts to target systems. It is built using OSGi and can be deployed in different topologies. The target systems are usually also OSGi based, but don't have to be.
When assembling software out of reusable components, the task of deploying software onto an ever increasing number of targets is not trivial to solve. This becomes even harder when these targets require different components based on who's using them. Apache ACE allows you to group those components and assign them to a managed set of targets. This allows you to distribute updates and new components easily, while keeping a full history of what was installed where during what period. It also helps you setup an automated development, QA/testing, staging and production environment.
Java Persistence API Implementation
Apache OpenJPA is a Java persistence project at The Apache Software Foundation that can be used as a stand-alone POJO persistence layer or integrated into any Java EE compliant container and many other lightweight frameworks, such as Tomcat and Spring. The 1.x releases are a production ready, feature-rich, compliant implementation of the Java Persistence API (JPA) 1.0 part of the JSR-220 Enterprise Java Beans 3.0 specification, which pass the Sun JPA 1.0b Technology Compatibility Kit. The 2.x releases are a production ready, compliant implement of the JSR-317 Java Persistence 2.0 specification, which is backwards compatible to the JPA 1.0 specification...
Commons Logging is a thin adapter allowing configurable bridging to other, well known logging systems.