Google has a rather large number of services, and with nearly each service comes an API that developers can use to integrate Google services with their apps.
Google has now released a new open source API client library for Microsoft’s popular .NET framework. The library currently supports not only Microsoft .NET 3.5 and 4.0, but also Mono (2.6.7 and higher). Mono is an open source implementation of Microsoft’s .NET framework and works on non-Windows OSs such as Linux and as well. Google may also release version of their library for Windows Phone 7 and Silverlight in the future.
Using this library one can add support for Google services such as Buzz, Books, Tasks, URL Shortener, Page Speed Online and many more. If you are a .NET developer, you can download the library from its project page on Google Code.