IApiExplorer is a new abstraction layer that allows you to obtain a description of the structure of your ASP.NET Web APIs. This interface also comes with a default implementation - APIExplorer.
Some of the things you can do with this API -
- Produce Documentation
- Create Machine Readable Metadata
- Create a Test Client
These posts from Yao (Microsoft) shows examples of how to use this API mainly for printing out the list of Web APIs and creating help documentation respectively.
Note that this is not available in the beta download of ASP.NET MVC – you will have to download the CodePlex bits to get the new functionality – Yao explains (paraphrasing) -
..this is new and not available in beta. But you can try it out using our Codeplex bits.
Henrik has a nice post on how to consume the package.
ASP.NET Web API is a new framework included in ASP.NET MVC 4 (currently in Beta) that makes it easy to build RESTful web services using .NET Framework. There are however other options - for instance, Service Stack which provides similar functionality and is already quite popular.