Usergrid - Turnkey social graph, activity streams for your application

Almost every application has a social layer these days. If you have users, most likely you have relationships, roles, and activity streams. Usergrid, a Java project from Apigee aims to be a turn-key platform to add these features to your application. If the thought of setting up Cassandra is intimidating, you can use their hosted version, which will also give you some analytics:

For more info check out the project web site, API docs, or source on GitHub.