One file simple usage WebApi selfhost (console program + Microsoft.AspNet.WebApi.SelfHost nuget). Needs to be run as admin.

program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Web.Http.SelfHost;
using System.Web.Http;

namespace ConsoleApplication1
{
    // listens to /api/foo/{id}
    public class FooController : System.Web.Http.ApiController
    {
        public string Get(int id)
        {
            return "Foo " + id;
        }
    }

    class Program
    {

        static void Main(string[] args)
        {
            var config = new HttpSelfHostConfiguration("http://localhost:8087");

            config.Routes.MapHttpRoute(
                "API Default", "api/{controller}/{id}",
                new { id = RouteParameter.Optional });

            using (HttpSelfHostServer server = new HttpSelfHostServer(config))
            {
                server.OpenAsync().Wait();
                Console.WriteLine("Press Enter to quit.");
                Console.ReadLine();
            }
        }
    }
}

Thanks for the code.

If you want to run a self-hosted API without admin permissions, for example when running a test, use the following:

var config = new HttpSelfHostConfiguration("http://localhost:80/Temporary_Listen_Addresses/Demo");

And access it via http://localhost/Temporary_Listen_Addresses/Demo/api/Foo/42.