   sharing the screen
  is it possible to have multiple applications rendering to the same screen (with hardware, mind you). and, does this have much process switching overhead that would make it slow? 
  by screen, do you mean display device(such as a monitor), or do you mean application window?  You can do the first, but not the second. ;  there is some overhead with having two applications rendering at once, since both need their gl state loaded, and the driver is going to have to switch between them  ;  Kind of interesting, I am actualy working on a UI that has multiple glviews.  Not sure what exactly that is on the windows side, but i have several instances of NSOpenGLView  in my window.  From there I can assign different camera objects to diferent views.  only problem is I am having some thread dificulty... at least i thin its with the thread.  The views do not update unless the window is resized or paret of the view itself goes off screen. then it updates that frame what ever it would be on while the game is running. ;  myahmac, it sounds like you aint consitantly repainting the window at the correct moments, when the window is resize or draw the paint event is called, thus triggering the updates, you need a way to force that update to happen correctly for each window. without more details on how your doing thing i cant be any more specific 