The Google Play Game Services Java Library allows developers to easily integrate the Google Play Game Services API into their Java applications. Developers can add the library to their Maven or Gradle projects using the code provided, or they can download the necessary jars as a zip file.
Yammer, a microblogging-for-business site and winner of the top prize at the recent TechCrunch50 conference, has released an API to allow developers to build their own applications around the service (Yammer API profile). Created by the people behind genealogy site Geni, Yammer has taken the tried and tested Twitter model, which asks users to answer the question "What are you doing?" in 140 characters or less, and adapted it for businesses, turning the question into "What are you working on?"
For those who get their kicks out of a good old physical board game, BoardGameGeek is a fun application that may be of interest. It's an online board gaming resource and community that is constantly updated in real-time by it's growing list of users. Users from across the world can participate in reviews, ratings and live discussion forums, add images, find play-aids, access session reports and more. BoardGameGeek also provides the BoardGameGeek API which means this functionality can be easily accessed and integrated with other applications.