The goal of the REST Starter Kit is to simplify the process of building RESTful services with WCF, without having to wait for .NET 4.0. Just to be clear there is no guarantee that what you can find today in the starter kit will end up in the .NET 4.0!
The REST Starter Kit is out since November 2008 and introduces a set of extensions to the WCF programming model that ship with .NET 3.5: a collection of Visual Studio templates that speed up the process of building certain types of RESTFul services and a new DLL that includes some new features for WCF.
Here is a list of the provided templates you can choose to install during the REST Starter Kit installation process:
If you are new to the REST Starter Kit Aaron Skonnard from Pluralsight has put together a nice screencasts for endpoint.tv that gives you a great introduction to the WCF REST Starter Kit:
The preview 1 of the WCF REST Starter Kit is available on Codeplex: