I would like to know if anyone has any idea how to lock the screen of a Mac while the desktop is still displayed. I have a Mac Mini with the presentation software ProPresenter running and I would like to lock the screen but still have the slideshow playing on the external (secondary) monitor. I tried a transparent screensaver and the default screen lock but it did not work because the screen turns black. I have found several applications that do this for Windows but none for Mac. If anyone has any idea what to do, help would be appreciated. Thanks.