program.cs

namespace SelfHost
{
    using System;

    using Microsoft.Owin.Hosting;

    using NancyKatana;

    class Program
    {
        static void Main(string[] args)
        {
            string url = "http://localhost:8989";

            using (WebApplication.Start<Startup>(url))
            {
                Console.WriteLine("Server running on {0}", url);
                Console.ReadLine();
            }
        }
    }
}

Startup.cs

namespace NancyKatana
{
    using Owin;

    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            app.UseNancy();
        }
    }
}