If you want to integrate Twitter into your ASP.NET website there is one API called twitterizer available (Open Source).
There are some projects developed using this API. you can view that projects from here
Here is the one of the tutorial written by Scott Mitchell to explain how to use twitterizer api in asp.net
Integrating Twitter Into An ASP.NET Website By Scott Mitchell
Twitter is a popular social networking web service for writing and sharing short messages. These tidy text messages are referred to as tweets and are limited to 140 characters. Users can leave tweets and follow other users directly from Twitter’s website or by using the Twitter API. Twitter’s API makes it possible to integrate Twitter with external applications. For example, you can use the Twitter API to display your latest tweets on your blog. A mom and pop online store could integrate Twitter such that a new tweet was added each time a customer completed an order. And ELMAH, a popular open-source error logging library, can be configured to send error notifications to Twitter.
Twitter’s API is implemented over HTTP using the design principles of Representational State Transfer (REST). In a nutshell, inter-operating with the Twitter API involves a client – your application – sending an XML-formatted message over HTTP to the server – Twitter’s website. The server responds with an XML-formatted message that contains status information and data. While you can certainly interface with this API by writing your own code to communicate with the Twitter API over HTTP along with the code that creates and parses the XML payloads exchanged between the client and server, such work is unnecessary since there are many community-created Twitter API libraries for a variety of programming frameworks.
This article shows how to integrate Twitter with an ASP.NET website using the Twitterizer library, which is a free, open-source .NET library for working with the Twitter API. Specifically, this article shows how to retrieve your latest tweets and how to post a tweet using Twitterizer.
Hope this will help