This is asp.net web api plugin for nopcommerce in order to expose REST style services. The zip files contains source + plugin itself.
Checkout video, you can create your own Web API plugin at Youtube
Please read the description here (http://dotnetdreamer.net/aspnet-web-api-services-in-nopcommerce) in order to know how it works.
The plugin also support web api versionning and dependency injection of autofac for asp.net web api.