Labltk is somewhat more primitive than Tk, but Tk still doesn't have native support for a tabbed interface, or notebook. This is a function which will make a widget that works pretty much like a tabbed interface.

open Tk

let create_notebook frames top =
  let tv = Textvariable.create () in
  let currentframe = ref None in
  let bounding = Frame.create ~borderwidth:2 ~relief:`Raised top in
  let buttonframe = Frame.create bounding in
  let bottomframe = Frame.create ~relief:`Groove bounding in
  let buttons = 
    List.map
      (fun (name,f) ->
        let f = f bottomframe in
        name,f,Button.create ~text:name ~command:(fun () -> Textvariable.set tv name) buttonframe
      )
      frames
  in
  let trd (_,_,c) = c in
  if frames <> [] then pack ~side:`Left (List.map trd buttons);
  let rec toggle () =
    (
     match !currentframe with
       None -> ()
     | Some f -> Pack.forget [f]
    );
    let b = Textvariable.get tv in
    List.iter
      (fun (n,f,button) ->
        if n = b then
          (
            Button.configure ~state:`Disabled button;
            if Pack.slaves f <> [] then
              Frame.configure ~borderwidth:2 bottomframe
            else
              Frame.configure ~borderwidth:0 bottomframe;
            pack [f];
            currentframe := Some f
          )
        else
          Button.configure ~state:`Normal button
      )
      buttons;
    Textvariable.handle tv ~callback:toggle;
  in
  Textvariable.handle tv ~callback:toggle;
  pack ~anchor:`W [buttonframe];
  pack ~fill:`Both ~expand:true [bottomframe];
  if buttons <> [] then Button.invoke (trd (List.hd buttons));
  bounding

Here is a function you can use to test it:

let test () =
  let top = openTk () in
  let frames =
    ["one",(fun f -> let f2 = Frame.create f in let l = Label.create ~text:"one" f2 in pack [l]; f2);
    "two",(fun f -> let f2 = Frame.create f in let l = Label.create ~text:"two" f2 in pack [l]; f2);
   "nothing",(fun f -> Frame.create f)]
  in
  let nb = create_notebook frames top in
  pack ~fill:`Both ~expand:true [nb];
  mainLoop ()