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.
An open source Atom implementation
The goal of the Apache Abdera project is to build a functionally-complete, high-performance implementation of the IETF Atom Syndication Format (RFC 4287) and Atom Publishing Protocol (RFC 5023) specifications.
A cloud computing platform for provisioning and brokering access to dedicated remote compute resources.
VCL is a modular cloud computing platform which dynamically provisions and brokers remote access to compute resources including virtual machines, bare-metal computers, and resources in other cloud platforms. A self-service web portal is used to request resources and for administration.
Support for Mono and Microsoft .NET development using Ant
This is a library of Ant tasks that help developing .NET software. It includes the "old" .NET tasks like a C# compiler task but also comes with support for NUnit testing or running the popular NAnt or MSBuild build tools.