Using the whole screen is possible on both OSX and Windows.
- Click "View" at the top of the screen, and uncheck "Basic Menu"
- Alternatively, click the little line above the menu bar and drag it around, the menu is now floating and you can make the OE-Cake window fullscreen
If you have OSX El Capitan, every "app" will be able to be forced full-screen as a new Space. This hides the menu bar, and dock, providing every pixel of the screen for use, but prevents the OE-Cake window updating in certain ways like changing the Scale automatically. Sadly the best solution is to press the "Option" key while pressing the fullscreen button, this will do the "old fullscreen" by resizing the window.