This hangout app will display a simple WebGL room and place an avatar for each participant in the room. The location/orientation of each participant is synced via the shared state of the hangout, so that everyone can see where the others are. There's also some basic collision checking.
Using the Google+ API to extract all kinds of statistics information about your public activities. You can check out a running version here: https://www.foldedsoft.at/+/allmy+/
This initial release is intended for feedback and learning - they are restricted to a courtesy usage quota and some functionality is disabled. This should provide enough access for you to check out the APIs and to start integrating Google+ with your apps. You can request more quota at the Google+ API Console.
The Google+ PowerApp lets you add a person to your circles right inside your emails. The app shows you a short summary of the particular user associated with that email, and lets you check off which circles you'd like them to be added to.
Are you new to the Google+ platform? If so, check out the main documentation page. To download client libraries or starter projects, visit the download page. If you're looking for help with the Google+ platform, visit the official Google group.