ExtremeSwank OpenID Consumer is a complete (and fully functional!) OpenID Relying Party written in C#. It is an independent implementation, and includes the following features:

• Completely compatible with web hosting environments (no unsafe code)
• Complete OpenID Relying Party supporting OpenID 1.1 and 2.0
• Supports both Stateless and Stateful modes
• Simple Registration, PAPE, and Attribute Exchange extension support included
• Plugin based architecture makes it easy to extend as more OpenID Extensions are created
• An extensive array of built-in persistence options (as well as a completely stateless option) makes it a cinch to integrate into your complex setup
• Targets .NET 2.0
• Add OpenID support to regular desktop applications using the new OpenIdDesktopClient