A recent project of mine has been ContribKanban.com for the Drupal community. The name speaks for itself - it provides a way for contributors to work on Drupal.org project issues queues through a kanban board. This app has two purposes: visualize the Drupal.org project issue queues in a useful fashion, and provide an experiment that tries to fully utilize Drupal.org APIs.
I've been hard at work in the labs revamping the Facebook Album plugin for WordPress. Very soon you will be able to use a Facebook application to authenticate with the Facebook API. That means you'll be able to embed personal albums into your WordPress site - and give me better ability to extend the plugin in the future.
Google+ has released a rough outline on their API for accessing data. The Google+ API only allows for read-access to data, but this will still allow you to integrate a visitors social features around Google+. API calls can either be completed via an API key or an OAuth 2.0 token for user data.The Google+ API follows a typical REST design involving HTTP GET on many API calls and the results are in JSON format.