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.