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.
Commons-Email aims to provide a API for sending email. It is built on top of the Java Mail API, which it aims to simplify.
Apache Karaf is an OSGi distribution for server-side applications.
Apache Karaf is a small OSGi based runtime which provides a lightweight container onto which various components and applications can be deployed.
Apache Deltacloud provides common front-end APIs to abstract differences between cloud providers.
Deltacloud contains a cloud abstraction API - whether the Deltacloud classic API, the DMTF CIMI API or even the EC2 API. Each abstraction API works as a wrapper around a large number of clouds, shielding users from their differences. For every cloud provider there is a driver "speaking" that cloud provider's native API, freeing you from dealing with the particulars of each cloud's API.