I have created an NHibernate second-level cache provider for AppFabric. For more information on why I have created this project please take a look at the Stack Overflow question I posted some 18 months ago. You can find all of the code on GitHub and in the coming days I am planning on creating a NuGet package for this project and fully documenting all the features either here or on GitHub, and detailing some of the features I plan to add in the future as well as adding some (more) tests.
I would describe this as a beta version currently, I am happy to support anyone who wants to use it but ultimately it is used at your own risk. I would appreciate any feedback including bugs and additional features.
Update: You can now install this with NuGet. The name of the package is NHibernate.Caches.AppFabric.
Update: I have documented all of the provider features here.