An X window manager is a window manager which runs on top of the X Window System, a windowing system mainly used on Unix-like systems. Unlike the Mac OS (Apple Macintosh) and Microsoft Windows platforms (excepting Microsoft Windows explorer.exe shell replacements) which have historically provided a vendor-controlled, fixed set of ways to control how windows and panes display on a screen, and how the user may interact with them, window management for the X Window System was deliberately kept separate from the software providing the graphical display. The user can choose between various third-party window managers, which differ from one another in several ways, including: customizability of appearance and functionality: textual menus used to start programs and/or change options docks and oth