IdentityServer with Sitefinity
If you haven't heard about IdentityServer yet, get on the band wagon. It's a great open light-weight security token service (STS) built using .NET 4.5, ASP.NET MVC4, WCF and Web API. You can quickly get enterprise-level SSO scenarios up and running. It's also quite easy to add custom claims and memebership management.
I had a pressing need to integrate it with Sitefiniy, so I forked IdentityServer on GitHub and added compatibility with Sitefinity. So far I've only tested it with Sitefinity 5.4 and 6.0. You can download the project below.
You can find the instructions on how to use it on my blog post here.