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 ServiceMix is an open source ESB implementing JBI.
Apache ServiceMix is an open source distributed Enterprise Service Bus (ESB) and SOA toolkit built from the ground up on the semantics and APIs of the Java Business Integration (JBI) specification JSR 208 and released under the Apache license.
Bean Validation API Implementation
The goal of the Apache BVal project is to deliver an implementation of the Java Bean Validation Specfication (JSR303) which is TCK compliant and works on Java SE 5 or later. The initial codebase for the project was donated to the ASF by a SGA from Agimatec GmbH and uses the Apache Software License v2.0.
Types that extend and augment the Java Collections Framework.