A very simple F# example using OWIN

program.fs

open System
open Owin
open Microsoft.Owin

let doStuff (x:IOwinContext) = 
    x.Response.StatusCode <- 200
    x.Response.WriteAsync "Hello!"

[<EntryPoint>]
let main argv = 
    use app = Hosting.WebApp.Start("http://localhost:4444", fun x -> x.Run(fun y -> doStuff(y)))
    Console.WriteLine("Lets go!")
    Console.ReadLine() |> ignore
    0