ASP.NET Identity - ASP.NET Identity is a membership-based software system designed for the authentication and authorization of the users via building an ASP.NET application.
Notopass - Share your accounts without giving username/password
DotNetOpenAuth - DotNetOpenAuth is a free-to-use compiled library that comes with the real support to your site visitor to login with the help of openIDs via getting control of the ASP.NET control onto the page.
1Password - 1Password can create strong, unique passwords for you, remember them, and restore them, all directly in your web browser.
BugMeNot - BugMeNot is a free Internet service that provides usernames and passwords to allow users to bypass the registration process for websites.
ShareAccount - Share your account without giving out your password