Message Bus is a cloud-native application service for email and mobile messaging. The selling point is the high deliverability rate, its ability to scale according to demand and the fact that it's simple enough to be used by developers with limited time and resources. The Message Bus API makes it possible for developers to easily add messaging functionality to their websites and apps.
Google Contacts API gives client applications access to a user’s contacts list where the application can create new contacts, update or delete existing ones, or query for contacts that match particular criteria. This tutorial explains how to implement the API in C# and ASP.NET with OAuth 2.0.