Xcode & Swift – Window without title bar but with close, minimize and resize buttons

The new window style mask NSFullSizeContentViewWindowMask added in OS X 10.10 will do the trick.

self.window.titleVisibility = NSWindowTitleVisibility.Hidden;
self.window.titlebarAppearsTransparent = YES;
self.window.styleMask |= NSFullSizeContentViewWindowMask;

Release Notes