As you are probably aware, Google took the Hangouts API out of preview last month. That means that anybody can mess around with Hangouts now to make their own Web applications that utilize what is arguably Google+'s most popular feature.
With any new API, developers are going to have questions. That's why the Google+ team held their usual Office Hours to discuss the API. You'll want to check out the video to get all the details on publishing a Hangout app, the terms of service for the API and the Hangout button. This is all very important stuff that any developer worth their salt should know.
The most interesting part of any Hangout is the Q&A session at the end. This week doesn't disappoint with some details emerging on the REST APIs and how to set the Hangout topic. The most important question though might be the very last one which covered whether or not you can use the Hangout button with other developer's Hangout apps. The answer is a resounding yes. As long as the Hangout app is public, you can share it however you like.
Check out the Hangout in full for all the juicy details on the Hangouts API. Become informed and start building some awesome apps.