http://stackoverflow.com/questions/24021624/in-gnu-emacs-osx-how-to-hide-title-bar

emacs-borderless.patch

diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index d9ad0a5..9e52d0f 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -446,6 +446,7 @@ minibuffer-prompt-properties--setter
         (ns-use-native-fullscreen ns boolean "24.4")
              (ns-use-fullscreen-animation ns boolean "25.1")
              (ns-use-srgb-colorspace ns boolean "24.4")
+             (ns-use-titled-windows ns boolean "25.2")
         ;; process.c
         (delete-exited-processes processes-basics boolean)
         ;; syntax.c
diff --git a/src/nsterm.m b/src/nsterm.m
index 1b44a73..d013101 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -6775,11 +6775,13 @@ - (BOOL)isOpaque
   maximizing_resize = NO;
 #endif

-  win = [[EmacsWindow alloc]
+  win = [[EmacsFSWindow alloc]
             initWithContentRect: r
                       styleMask: (NSResizableWindowMask |
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7
-                                  NSTitledWindowMask |
+                                  (ns_use_titled_windows ?
+                                   NSTitledWindowMask :
+                                   NSWindowStyleMaskBorderless) |
 #endif
                                   NSMiniaturizableWindowMask |
                                   NSClosableWindowMask)
@@ -6812,6 +6814,7 @@ - (BOOL)isOpaque
   [win setTitle: name];

   /* toolbar support */
+  if ( ns_use_titled_windows ) {
   toolbar = [[EmacsToolbar alloc] initForView: self withIdentifier:
                          [NSString stringWithFormat: @"Emacs Frame %d",
                                    ns_window_num]];
@@ -6833,6 +6836,7 @@ This avoids an extra clear and redraw (flicker) at frame creation.  */
   }
 #endif
   FRAME_TOOLBAR_HEIGHT (f) = 0;
+  }

   tem = f->icon_name;
   if (!NILP (tem))
@@ -8759,6 +8763,12 @@ Nil means use fullscreen the old (< 10.7) way.  The old way works better with
 This variable is ignored on OSX < 10.7 and GNUstep.  */);
   ns_use_srgb_colorspace = YES;

+  DEFVAR_BOOL ("ns-use-titled-windows", ns_use_titled_windows,
+     doc: /*Non-nil means to include a title on windows.  Nil means to
+omit the title on OSX >= 10.7.  This variable is ignored on OSX <
+10.7.  Default is nil.  */);
+  ns_use_titled_windows = NO;
+
   /* TODO: move to common code */
   DEFVAR_LISP ("x-toolkit-scroll-bars", Vx_toolkit_scroll_bars,
           doc: /* Which toolkit scroll bars Emacs uses, if any.