Google+ is set to get richer as Google today announced the release of the Google+ API. They had kept the API with them, developing the +1 button, circles, hangouts, games and while doing all that on your own, the idea to let it out in the open and allow the countless developers to play with it is something that ensures a viral growth.
The current API is currently focused on the Public data only, meaning that it only allows you to make use of all information of the Google+ users that has been made public by them. Since this has only started, users or anyone making use of the API needs to have you register your app before you are allowed to make requests.
The API opens up a lot of potential for Google to see Google+ thrive and grow quick. And just the way it is with Google, letting the masses have access to these APIs [of developers] opens up the possibilities of seeing more variety in the products and applications on the Google+ platform. Hopefully it will help them populate the network that has a lot of potential to grow significantly enough to have a presence against Facebook.
You can learn more about the API here.