OpenID - OpenID is a safe, faster and easier way to log in to web sites.
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.
Portier - An email-based, passwordless authentication service that you can host yourself.
ASP.NET SAML - ASP.NET SAML is an open-source authentication utility that has been used for exchanging authentication and authorization data between the channels.
IndieAuth - IndieAuth is a way to use your own domain name to sign in to websites.
BugMeNot - BugMeNot is a free Internet service that provides usernames and passwords to allow users to bypass the registration process for websites.