There are a lot open source initiative happening for the open social application development.Apache shindig is an incubator project helps to develop opensocial containers .
The dependency injection framework from Google.It helps in developing custom handlers in shindig.It takes creating instances in the form of Services from the Application client code and the Dependency between the Clients to its Services is automatically injected through some easy injection configuration mechanism.
The popular resusable components.
Extends java.lang functionality
Maps java beans to XML
For encoding decoding algorithms (base64 etc) utility.
The security protocol.I have written about oauth here
Replaces java date and time.
Implementing ATOM protocol and syndication.Its all about data in google..
The popular build tool.Commonly used project management tool for open source projects.Build,manage dependencies,update and so on.Very flexible.It appear as many things ..
Jetty is used to run sample applications provided with shindig.