I was reading the Modern Operating Systems book and it says
Many UNIX users, especially experienced programmers, prefer a command- based interface to a GUI, so nearly all UNIX systems support a windowing system called the X Window System (also known as X11) produced at M.I.T. This sys- tem handles the basic window management, allowing users to create, delete, move, and resize windows using a mouse. Often a complete GUI, such as Gnome or KDE, is available to run on top of X11, giving UNIX a look and feel something like the Macintosh or Microsoft Windows, for those UNIX users who want such a thing.
What operating systems are the most used by experienced programmers and UNIX users?