List of Free code OAuth2

FaceSharp - .NET Facebook SDK and Starter Kit
Join the .NET Movement in Facebook Apps. Actively developed, community supported and CURRENT. It's got what you need - OAuth2.0 / Graph API / Places / Insights Developed in C#
Google OAuth2
Google OAuth2 is a small library that uses the WebBrowser control in order to do simple authentication with a Google account.
ImapX 2
ImapX 2 is a crossplatform IMAP library for .NET, supporting SSL/TLS, OAuth2 and all major GMail IMAP extensions.
OAuth2 Authorizer
OAuth2 Authorizer helps you get the access code for a standard OAuth2 REST service that implements 3-legged authentication.
Yammer.SimpleAPI
Class use to interoperate with Yammer through Rest API and OAuth2 authentication