Giraffe - https://github.com/giraffe-fsharp/Giraffe

MinimalAspNetCore30WithGiraffe.fs

open Microsoft.AspNetCore.Hosting
open Microsoft.Extensions.Hosting
open Giraffe

let webApp = GET >=> route "/" >=> text "Hello world"

[<EntryPoint>]
let main args =
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(fun webBuilder ->
            webBuilder.Configure(fun app ->
                app.UseGiraffe(webApp) |> ignore
            ) |> ignore
        ).Build().Run()
    0

open Giraffe
open Saturn

let app = application {
    use_router (GET >=> route "/" >=> text "Hello world")
}

[<EntryPoint>]
let main _ =
    run app
    0

;-)

Damn! That's hot